The Thing is a 1982 horror film directed by John Carpenter and reunites him with his Escape from New York star Kurt Russell. The film is a remake of the 1951 classic The Thing from Another World and a prequel to this film was released in 2011.
The following firearms can be seen in the film The Thing:
A Heckler & Koch HK93 semi-auto rifle with a scope and a 40 round magazine is used by the Norwegian with Rifle (Kurt Russell's brother-in-law at the time of filming Larry Franco) to try and kill the infected dog while flying from the helicopter. When the helicopter lands the passenger (named Jan Bolen in a deleted scene) emerges with the rifle and continues after the dog while the pilot has a mishap with a grenade. Incidentally, this scene has in part been reproduced for the prequel, and the passenger renamed Lars.
Ithaca 37 shotgun
MacReady (Kurt Russell) carries a Ithaca 37 shotgun several times in the film. At one point Windows (Thomas G. Waites) manages to grab one before he is subdued by the others.
Garry (Donald Moffat) carries a Colt Trooper MkIII in a holster on his duty belt. Midway through the film MacReady (Kurt Russell) gets possession of Garry's revolver and carries it with him from then on.
M2A1-7 Flamethrower
This flamethrower is used by several members of the team throughout the movie. Palmer uses a different flamethrower, apparently a propane powered model sold commercially, used for burning weeds, and removing ice from planes and other equipment; the flame on the propane model is very short, at most usually 7 feet. Even so, many scenes in the film use genuine, military-spec liquid-fuelled flamethrowers, something of a rarity in movies.
MacReady (Kurt Russell) and some other survivors are seen using dynamite bundles to combat the alien. Most notably when MacReady grabs a bundle so nobody will they attack or burn him. The survivors fashion the dynamite to their chests with a improvised holder. (In the second photo under Molotov cocktail below, you can see the survivors are using WW2 Thompson magazine pouches to hold the dynamite)