Full Inventory:
Bring up the Map screen. Then press Left until the arrow is pointing at you. Press Start to return to the standard view. During the camera's auto-rotation, press L1, Square, X, and Circle at the same time. Press Triangle to verify that you have all of the weapons.
Invincibility:
Make sure you have the drill. Bring up the "Weapon Select" menu. Select the Frying Pan with L1 or R1. Go back to the game. Then go back once more into the Weapon Select menu. Press Circle and R1 to increment the selcted weapon until you get the flashing 999 on your health counter. You can also turn it off by holding Circle and R1.
Ammo Refill:
Get in the "Foot Mode". Do a backflip by pressing Square and L2. During the blackflip (before you land), press Right, X, and Circle at the same time. Now all of your weapons should have a weapon count.
Health Refill:
Get in "Foot Mode". Do a backflip by pressing Square and L2. During the backflip (before you land), press Down, X, and R2, at the same time.
See Final Sequence:
Select "Load Game" from the Main Menu. Press Right and hold it. While holding the Right press Circle. Press Triangle to cancel. Press Square and Left at the same time then let go. Press Triangle to cancel. Now the game will show the final Kitchen scene.
Fart Sounds for Butts:
Select "Load Game" from the Main Menu. Press R1, R2, L1, and L2 at the same time and then let go. Exit this screen. Now in the game, the butts will have a fart sound when they fire at you.
Turn On Collision Detection:
You must be in Jet Pack Mode. Find any dead body and stand over it. Now, press Triangle to bring up the weapons menu. Simultaneously press Right, Down, and L1. You should fall through the floor....use the jet pack to keep from falling.
Turn Off Collision Detection:
Press Triangle to bring up the weapons menu. Simultaneously press Right, Down, and L1.