Enter the following codes at the main menu. The sound of a chicken squawking will confirm that you've entered the code correctly. Then, press Square + Circle at the same time to bring up the active cheats screen.

R2, L2, R1, R2 God mode
L2, L2, R1, L1 all tracks
R1, L1, L2, L2 unlimited special weapons
L1, R1, L1, L2 unlimited missiles
L2, R2, L2, R1 unlimited turbo
L1, L1, L2, L1 RC boat mode
R1, R1, R2, L2 Chicken mode
R2, L1, R1, R1 big waves
R2, R1, R1, L1 access level 2 boats
L1, R2, L2, L1 access level 3 boats