Full Health
Press Start to pause game play, then press L1, R2, L2, R1, Up(2), Left, Square, Right, Circle, Start.
Shrink Jamgut
Press Start to pause game play, then press R2(2), Circle, R2, L2(2), Left, L2, Triangle.
Bonus Gallery
Press Triangle, Up, Circle, Right, Down(2), Square, Left at the main menu. Repeat this code to unlock more bonus gallery entries.
Alternate Ending
Successfully complete the game after saving all 260 natives to view an alternate cliffhanger-type ending.
Jackpot
At that weird dark place where you have to shot your boomerang at those light things to unlock the door there is going to another one with six instead of five. When you finally open it you get the jackpot.