Pressing 'D' and then 'N' activates cheat mode. Then enter any of the following codes:

CORNHOLIO-Turns God mode on or off and gives you unlimited jetpack fuel
KROZ-Turns God mode on or off and gives you unlimited jetpack fuel
COSMO-Gives you unlimited jetpack fuel
STUFF-Gives you all the weapons, keys and full ammo
ITEMS-Gives you all of the items and keycards
SCOTTY # (episode) # (level)-Warp to a level
CASHMAN-Makes you spew money
VIEW-Gives you a third-person view of Duke
RATE-Displays current frame rate
SKILL#-Changes the skill level
HYPER-Get high on steroids
Type 'D','N', then WEAPONS. This is similar to STUFF, but without the items (Jetpack, Medkit, Steroids, etc,.)