Mauser Karabiner 98 (98K) was the standard weapon for all German ground forces during World War 2.
Lee-Enfield No 4 Mk 1*
Used by all British Troops, mostly the Grenadier Guards in the Armored Column as well as the British 1st Airborne Division when they were trapped in Arnhem. The No 4 Mk 1* rifle was also seen in the hands of the Polish Airborne brigade troops.
M1 Garand
Used by American troops.
M1 Carbine
Used by American Soldiers and mounted on jeeps and other vehicles. Most notably seen when James Caan pulls one out of it's Jeep mount when he is hiding from a German Patrol in the Forest. Also used by Elliott Gould when leading the charge to capture a bridge.
M1911A1
Used throughout the movie, especially by James Caan when threatening a 101st Airborne combat surgeon (Arthur Hill) in order to get him to treat his wounded lieutenant (Nicholas Campbell).
Used by British Armored troops mounted to their Lend Lease Sherman Tanks.
Sten Mk5
The standard submachine gun for British and Polish Airborne units. Differentiated from earlier models by the wooden vertical foregrip and wooden stock.
No2 Portable Flamethrower
Used in the attack on the German bunker on the Arnhem bridge this weapon, known as the "Lifebuoy" for its' resemblance to a lifesaver, was the standard British flamethrower.
PIAT
Projectile Infantry Anti-Tank
Used throughout the movie by British and Polish airborne units (who were similarly equipped) this weapon fired a 3 lb. hollow charge warhead via means of a powerful spring which ignited it's propellant. The weapon had a powerful recoil which necessitated it being fired prone since any other position would knock the user flat down. Seen especially during the repulse of the initial German assault on the Arnhem bridge.