hmm...too many variables to pick just one...
Melee: Ripper from Fallout 3 or the Chainsword from the various Warhammer 40k games. None of this improbably and clumsy chainsaw bayonet bullcrap

Pistol: Falcon 2 from Perfect Dark or the DD44 from Goldeneye
SMG: The Submachine gun from Red Faction (fires both 12mm and 5.56 ammo) or the 10mm SMG from the Fallout series
Rifle: either the AK-47 clone from Perfect Dark Zero (because of it's air-powered bayonet launcher) or the K7 Avenger from Perfect Dark
Explosives: Remote Mines (Goldeneye/Perfect Dark)