Press ‘T’ on the keyboard and enter the following cheats:

antioch: 		kills all enemies
excalibur: 		All weapons    
igotbetter: 		health 100%
knight: 		god mode
mallrocks: 		infinite ammo  
rabbit: 		shields 100%
rambojet: 		gives you a jet
runaway: 		fires all weapons at once
shrubbery: 		gives you powerups
swallow: 		full gas
unladensswallow:	infinite gas

Thanks to Revolution readers Andrew Hema and Martijn Michiels!