Well, without the Dart Gun, Deathclaws will **** you up almost every time.
The Deathclaw Gauntlet is only really useful if you're specializing in unarmed attack.
The Nuka-Grenade, while devastating, has plenty of other explosive weapons that can do the same job. (Plasma grenades, etc)
Bottlecap Mines, same story. Plasma and frag mines, if your explosives' skill is high enough, can have nearly the same effect.
The Rock-It Launcher...is just mindless fun. Not very effective most of the time, and terribly innaccurate. Also, it's a pain to lug around all the crap to load it with just in case. It weighs you down pretty badly.
The Shishkebab is only good for people spec'd in melee attacks, and is deceptively poor unless you take the Pyromaniac Perk. But still, it's pretty awesome at higher levels. But hardly necessary.
The Railroad Rifle. That is all.
So, in conclusion: the Dart Gun seems like the only one that you actually need. The rest are just super-awesome fun.