Not a Remington Model 31 as prevously mentioned. You can tell it is a Ithaca 37 because of the lack of an side ejection port. It is also used to shoot the dogs and Windows manages to grab one before he is subdued by the others. MacReady (Kurt Russell) is also seen with one at the Norwegian base.
Garry (Donald Moffat) uses the Colt Trooper MkIII to shoot the Norwegian when he is trying to kill the infected dog with the H&K 93. The revolver was prevously thought to be a S&W Model 15, however the M15 is similar in looks. The Colt has a shrouded ejector rod housing, the M15 does not. The pictured revolver has the shrouded ejector rod unlike the S&W M15.
This flamethrower is used by several members of the team throughout the movie. Palmer uses a different flamethrower. The "other" flamethrowers appear to be those propane powered models sold currently, used for burning weeds, removing ice from planes and other equipment, the flame on those is very short though, at max usually 7 feet.
It can not be conclusively said to be a Thermite grenade but this can be assumed due to the cylinder shape and the explosions produce a lot of sparks. We also know that the Norwegians had Thermite charges. This grenade is used by one of the Norwegians. It slips from his hand, and on explosion it kills his colleague and destroys the helicopter.
MacReady and some other survivors are seen using what apears to be Dynamite. Most notable when MacReady grabs a bundle so nobody will they attack or burn him. The survivors fashion the dynamite to their chests with a imporsived holder.
