Cheat menu:
Press Left, Circle, X, Right, Circle, X, Down, Circle, X during game play. A cheats menu will appear with the following options:

Ponder: Turn AI off.
Gamewon: Jump to next level.
Invincible: No damage.
Coords: Displays current position.
Pal mode: Switches NTSC to PAL, will freeze NTSC machines.
Supermap: Display full map of current level.
Maxout:All weapons and ammunition.
Pogo: Higher jump to reach previously inaccessible locations.

To use the level skip feature, enable the "Gamewon" option on the cheat menu. Resume playing and pause the game to access a new option to jump to the next level.

Level select:
Enter X7P!45QX39 or P3NDLDQNY2 as a password to access all previous levels. Note: Enter 205F6HJT0V as a password to unlock all the levels and have all the guns.

Free batteries
You will see little box droids moving around on the floor. Shoot these little droids to get batteries for your flashlight and other objects that use them.