Federation Ground Equipment
When Captain Sisko beamed down to AR-558, we discovered that a Starfleet garrison had held a Jem'Hadar communications relay for five months. A Starfleet garrison. This was not a team of naval officers who had been accidentally stranded on a planet, or who had gotten pulled into combat on an away mission. One hundred and fifty men had beamed down with orders to take and hold an enemy installation, and they were from Starfleet. They wore Starfleet uniforms. They complained that the length of their stay exceeded "Starfleet regulations". After asking for an air evac for months, they didn't say one word that hinted of inter-branch bitterness (can you imagine what a real-life army commander would say if his unit had been abandoned on some faraway rock for months, and an Air Force captain showed up to tell them that they would have to wait a little longer?) This is canon proof that the Federation's deplorable neglect of their ground army, which has become more and more apparent with each missing category of ground weapon, is not merely the result of a weak army; it is the result of a nonexistent army. Starfleet is their army, so it should not come as a surprise to discover that their inventory of ground equipment is just as inadequate as their inventory of small arms, artillery, and armour.
Grenades
No hand grenades have ever been seen or even mentioned in the entire series runs of Star Trek TOS, TNG, DS9, or Voyager. They could theoretically jury-rig a phaser on overload to act as a crude hand grenade, but this is a horrendous solution for many reasons:
If a soldier has to throw his handgun away in the middle of combat in order to simulate the effect of a grenade, then he will be left without his weapon! Even if it's only his backup gun, it's hardly a good idea to throw it away.
Soldiers don't get issued more than one handgun, because this isn't a "proper" use of the weapon. Real grenadiers, on the other hand, generally carry large numbers of grenades.
Since the overload is actually a malfunction rather than a design feature, there is probably no guarantee that its delay timer is predictable enough to be used as a grenade. The overloads in "Conscience of the King", "The Hunted" and "The Next Phase" had much different delay times.
Since it was never designed as a grenade, with no fragmentation shell, it is ineffective as an anti-personnel weapon. Ro Laren and Geordi Laforge were uninjured by a nearby overload in "The Next Phase", and the effect of an overload in "The Hunted" was consistent with an HE explosion. HE grenades (ie- concussion grenades) are poor anti-personnel weapons in real life, and "The Next Phase" showed this to be the case in Star Trek as well.
However, while the Federation appears to have no hand grenades, they do seem to have something which seems to resemble a grenade launcher (note that this does not mean they must have hand grenades; real-life grenade launchers use specialized grenades). When confronted by So'na soldiers who were well out of hand phaser range, Worf used a weapon that looked very much like a modern LAW (see below).
However, if it was really a LAW, then the fact that he used it against foot soldiers is difficult to explain. A real soldier does not pull out a LAW when he see a handful of enemy soldiers in the distance! When the shell hit its target, it caused a small explosion which killed the entire group of soldiers (who inexplicably stayed in a tight cluster and exposed themselves to fire despite the easy availability of cover), as seen below:
This kind of explosion is what we might expect from a modern fragmentation grenade. There is no huge fireball or shockwave, and the tiny fragments produced by the blast would kill the So'na without being visible from a distance. Therefore, the weapon appears to be an anti-personnel RPG. Trekkies are liable to claim that it had "yield settings" and was not used at full power, but it is unreasonable to claim the existence of capabilities which have never been observed or even suggested onscreen. Yes, it might be capable of more. Yes, the Federation undoubtedly has the technological werewithal to produce more powerful ground weapons. But no, there is no evidence that they have actually done so. This weapon is obviously designed to extend the fighting capabilities of Federation ground troops beyond the limitations of their pitiful small-arms arsenal, by giving them an equivalent of the modern M203 40mm grenade launcher (which is normally mounted to the underside of an M-16 assault rifle or M-4 carbine). However, it is actually inferior to the M203, since it is much larger without adding any more destructive capability.
Grenades are relatively indiscriminate weapons of killing or destruction, and it's possible (perhaps probable) that this aspect of their nature made them politically unpalatable in the Federation. It may be that the Federation frowns upon weapons which don't require precise, deliberate action for each and every enemy casualty. A line-of-sight grenade launcher makes sense in this environment, since it requires precise, deliberate action. A man can't simply throw it into a compound, wait for the explosion, and then rush in to see whether he killed anybody.
So why would the Federation develop a grenade launcher when they have blatantly neglected virtually every other type of ground weapon, save small arms? Why would they develop a grenade launcher when they don't even have a sustained-fire support weapon, and when they've taken mortars out of their inventory? Why would they bother, when their approach to ground combat is to be completely dependent on air support? The reason is obvious: the Borg. The Enterprise-E was nearly overrun by Borg drones in STFC, and since Starfleet designs its weapons around the priorities of starships rather than ground armies, this near-disaster finally prompted them to develop a fragmentation weapon. The Borg are slow, they move in tightly clustered groups, and they have so little body armour that they couldn't survive low-velocity Thompson SMG bullets. Therefore, when the STFC post-mortem was being performed at Starfleet Command, the admiralty probably realized that they needed a fragmentation-based anti-personnel weapon. However, their phasers aren't capable of blasting lethal shrapnel out of walls the way Imperial Blastech E-11 carbines can, so they had to use grenades, while respecting their cultural prohibitions against indiscriminate weapons. The answer? A grenade launcher, which appeared three years later.
It is unfortunate (to say the least) that Starfleet controls the entire Federation military, since a dedicated ground army would have undoubtedly demanded this weapon long before the near-disaster of STFC, and it would also demand artillery, armour, sustained-fire support weapons, and a whole host of other weapons so that they'd have a chance of survival.
Flamethrowers
No Federation flamethrowers have ever been seen or even mentioned in the entire series runs of TOS, TNG, DS9, or Voyager. It goes without saying that flamethrowers, which have been outlawed in real life, would probably be outlawed in the Federation as well, and for similar reasons.
Anti-Tank and Anti-Aircraft Weapons
No Federation anti-tank or anti-aircraft weapon has ever been seen or even mentioned in the entire series runs of TOS, TNG, DS9, or Voyager. Starfleet's philosophy regarding fortifications, enemy armour, or aircraft seems to be "we'll handle it from the air". Federation ground armies seem to be like baseball players; they can only come out to play when it's sunny outside.
Note: The standard Trekkie rationalization for their lack of anti-armour and anti-aircraft weaponry is to claim that a hand phaser can vapourize armour or bring down aircraft (sadly, I'm not being sarcastic; they really say this). However, that is nothing but wishful thinking. Their hand phasers have never demonstrated the ability to punch through armour plating. We saw them blast chunks of rock in TOS episodes such as "Where No Man Has Gone before", TNG episodes such as "Chain of Command", and DS9 episodes such as "Nor the Battle to the Strong". We saw them blast ceramic pottery in "The Omega Glory", and we saw them make organic matter disappear into thin air in countless episodes of TOS, TNG, and DS9. But rock, ceramics, and flesh are not metallic armour. Flesh is a low-density material which is mostly composed of water. Ceramics and rock are low-density materials with poor thermal and electrical conductivity. Metallic armour, on the other hand, is a relatively dense material with excellent thermal and electrical conductivity. The material-dependent nature of phasers is well-established, and their effectiveness against armour is pure Trekkie supposition.
There have been countless incidents of shipboard combat throughout TOS, TNG, DS9, and Voyager, but they have never blasted gaping holes in the thin walls. Extended high-power phaser blasts were fired at an inactive shuttle in "Lower Decks" (in order to make it look as if it had been damaged), and they produced nothing but small scorch marks. Men used packing crates as cover against phaser fire in episodes such as "Too Short a Season" among others, and enemy phaser fire couldn't penetrate them. So if phasers are so effective against armour, then why were they so ineffective in these situations?
If you want to see the effectiveness of military guns in a metal-lined environment, watch Han Solo, Luke Skywalker, and Chewbacca when they break into the Death Star detention centre. Within seconds, the room is choked with smoke from metal that was vapourized off the walls by blaster hits, and large chunks of the ceiling can be seen falling to the floor where Chewbacca is firing his rifle. Men are even killed by the shrapnel which is thrown away from blaster hits on the walls, in this scene as well as another scene later in the film. In TPM, shots from small handguns blast the legs, arms, and heads off battle droids. Have similar effects ever been observed when phasers were discharged on board a starship? No.
Federation phasers are not anti-armour weapons. Instead, their behaviour is clearly target-dependent; they make organic matter disappear into thin air, they have the effectiveness of blasting charges against rock, and they have almost no effect at all on metal, unless it's extremely thin (eg. a cooking pot). This is not supposition or theoretical musings based on the well-established NDF chain reaction; it is simple observation. Against flesh, phasers are almost like magic. Against rock, phasers are like grenade launchers. Against metal, phasers are like pop guns. Trekkies usually try to explain this consistent pattern away by making vague reference to "yield settings." However, no intelligent observer could possibly accept this explanation. The sheer consistency of this pattern demands an explanation, just as consistent patterns demand explanation in real life. Moreover, that explanation must be more logical than the absurd notion that they deliberately set their weapons in such a manner as to consistently simulate a pattern of material dependency (even when it costs them a battle), and the only logical explanation is that this pattern is simply part of their nature. Therefore, against any armoured vehicle (never mind an enormous, lumbering AT-AT walker), the only real use for a hand phaser would be for suicide, to prevent capture.
As for the idea that small arms can be used as anti-aircraft weapons, that is simply ridiculous. Unless an aircraft stops and hovers at low altitude, a human being has almost no chance of hitting it with small-arms fire, regardless of how accurate his gun is. Only robotics and computerized targeting systems can hope to hit a fast-moving aircraft, even with automatic fire and proximity-fused fragmentation ordnance.
Mines
No Federation land mines have ever been seen or even mentioned in the entire series runs of TOS, TNG, DS9, or Voyager. Given the controversy over the ethics of land mine deployment in real life, it seems self-evident that they are probably outlawed in the politically correct Federation.
Body Armour
No Federation body armour has ever been seen in the entire series runs of TNG, DS9, or Voyager. They seem to ignore the possibility of shrapnel from concussive explosions (a mistake which undoubtedly came back to haunt them when the Klingons started using mortars), and silly theories about shrapnel-resistant uniforms don't hold up well against episodes like "Who Watches the Watchers". However, to be fair, it is possible that the thick leather vests and jackets worn by Captain Picard and certain ground troops are designed to resist knife and shrapnel puncture wounds, since hand to hand combat occurs so often. But why no helmet? Real-life armour is designed to prevent fatalities; the head and chest must be protected, since wounds to the rest of the body tend to be crippling but not fatal. A man without a helmet is not ready for battle.
Interestingly enough, a man with a helmet was seen once in Star Trek (specifically, in ST:TMP), but only in Kirk's more militarized era (which only makes sense). As an off-topic aside, the rise and fall of Federation militarism could actually be an interesting subject for study. In TOS the Federation was an aggressive, expansionist colonial power, which found itself engaged in a long, bitter cold war with the Klingon Empire over the control of intervening territory. They had heavier ground weapons, and truly military vessels (no comfortable lounge chairs on the bridge, no children running around underfoot, no anti-military rhetoric, etc). Far from slavishly adhering to their Prime Directive, they regularly meddled with the affairs of primitive races inhabiting planets of strategic interest, often under the guise of combating Klingon aggression. They appeared to be very successful, and by the time of ST6, their military position was so strong that Colonel West confidently preached war, explaining: "Frankly, Mister President, we can clean their chronometers". Then the Klingons signed an historic peace treaty, the Romulans were nowhere to be seen, and a long period of comfort and complacency began to set in.
Eighty years later, the Federation appeared to have become desensitized to its surroundings, with happy, complacent, over-educated citizens spending their days in idle contemplation or holo-simulated hedonism. The military had grown in societal prominence, but it had lost its focus. Where once its mission was clear (to protect the Federation and promote its strategic and interests), its mission was now heavily diluted. Their original doctrine of aggressive colonial expansion under the guise of "exploration" was now interpreted as a sincere desire to abandon military ways and means in favour of exploration solely for the sake of knowledge. The simmering tension between military officers and civilian government officials that we saw in TOS was now gone: the military and the civilian government were now virtually one and the same (see the Canon Database for numerous examples). Collectivism and communism became the reigning socio-political mindset, and military personnel were even encouraged to risk the safety of their families for king and country, by making them permanent residents of their military vessels! But in all this foolishness, the importance of military readiness was somehow lost.
It is not surprising, given this context, that their ground army (now an lowly arm of Starfleet), was grossly under-equipped. They actually ordered their men into battle with nothing but a padded leather vest for protection and no helmet whatsoever, and like the obedient soldiers who charged over the top into enemy machine-gun fire in WW1, they dutifully obeyed.
NBC Protection
No Federation NBC suit has ever been seen or even mentioned in the entire series runs of TOS, TNG, DS9, or Voyager. Their approach to radiation appears to be the scientifically ludicrous use of "innoculants". Their approach to biological and chemical hazards seems to be reparative rather than preventive; they actually allow themselves to be injured or infected, and then they attempt to repair the damage afterwards! This is incredible; are they supposed to beam out of any dangerous situation whenever they're exposed, and then stagger to Sickbay before succumbing? What if a theatre shield, a transport scrambler, sensor jammers, unusual planetary magnetic fields, or atmospheric electrical storms prevent transport? What about the time factor? Is a soldier supposed to call for an emergency beam-out after being exposed to real-life chemical weapons which can leave you incapable of articulate sounds in 8 seconds, unconscious 9 seconds later and dead less than 3 minutes after that? What about Imperial Fex-M3 nerve gas, which supposedly kills in 10 seconds? Federation soldiers would be slaughtered wholesale by chemical weapons, and ruthless armies like the Imperial army would not hesitate to take advantage of this fact.
Even their quasi-magical "radiation innoculant" is hardly omnipotent. It appears to have reparative capabilities, but it can't do anything about radiation which is intense enough to cause prompt and deep burns (no one showed any signs of skin damage even when they were mere seconds away from the point of no return in "Booby Trap"). Furthermore, no amount of repair will prevent death if the cause of irradiation is not removed. In "Booby Trap" as well as other incidents, it was made quite clear that while their quasi-magical "innoculant" (all hail their scientifically ignorant soap opera writing staff) can repair and delay radiation damage, it won't do much good if they don't remove themselves from the source of the radiation. But the prompt radiation produced by the blast itself (the type which they invariably worry about) is actually not the biggest threat, particularly for soldiers who might be inside shielded or armoured structures. The intense, ionizing radiation produced by the blast itself tends to be absorbed and retransmitted at lower energy levels by atmospheric gas particles, so that by the time it reaches you it has been mostly converted into heat and work (ie. shockwave, fireball). But modern tactical nuclear devices tend to be low-yield and "dirty", meaning that they produce a lot of dangerous fallout and they aren't powerful enough to blast most of it up into the upper atmosphere (where it will lose most of its radioactivity before falling back to Earth). The fallout isn't dangerous enough to kill you from a distance, but it gets absorbed into your lungs, it enters the pores of your skin, it get into your eyes and ears, and once it's inside your body, it emits various forms of radiation which slowly destroy your body from within.
That is why Hiroshima and Nagasaki survivors who felt good enough to work in the relief efforts usually tended to have a lower chance of survival than those who were rendered immobile; the stronger survivors' increased activity levels led to increased respiration and increased intake of radioactive fallout, while the immobile survivors tended to lay still, breathing lightly and slowly. If you survive the short-term effects of the blast itself, your biggest worry afterwards is the fallout, not direct radiation. If you inject this ridiculous "innoculant" into a Federation trooper who absorbed large quantities of radiogenic materials into his body, it would only postpone his slow, agonizing death rather than preventing it. The real threat is the fallout that continues to irradiate his tissues and internal organs, and unless this can be removed somehow, the soldier will die. Is this really a better idea than an NBC suit?
The Federation's approach to NBC warfare is to simply ignore the possibility. They have no protection against chemical or biological weapons apart from the hope that they can get to Sickbay before it kills them. They have no protection against radioactive fallout except their ridiculous "innoculant", which is useless against very intense radiation and which would provide only a temporary stay of execution for a man who has ingested radiogenic fallout. Therefore, they would not survive battle against an enemy willing to use NBC weapons.