Cheat for All Weapons w/ Full Ammo:
Pause during game and press L2 + R1, X, O, UP, Up, Square, Down.

GameShark Codes

Have Machine Gun
300f095a0063 
  
Have Dynamite
300f095b0063 
 
Have Grenades
300f09560063 
 
Have Rocket Launcher
300f09570063 
  
Have Bazooka
300f09580063 
  
Have Flamethrower
300f09590063 
  
Have Land Mine
300f095c0063 
  
Have Medpaks
300f095d0063 
  
Have Mine Detector
300f095e0001 
   
Have Binoculars
300f095f0001 

Thanks to Revolution readers Gomer P. and Sam!