Invincibility
Pause the game and press Triangle, Triangle, Circle, Circle, L1, L2.

All weapons
Pause the game and press Square, Square, Circle, Circle, L1, L1.

Infinite ammunition
Pause the game and press L1, L1, R1, R1, Circle, Circle.

Slow rockets
Pause the game and press L1, R1, R1, L1, Triangle, Square.

Auto-reload
Pause the game and press Square, Square, Triangle, Triangle, Circle, Circle.

Slow-mo mode
Pause the game and press Triangle, L1, Triangle, L1, Triangle, L1