Cheat mode
At the title screen, press Left, Right, L1, R1, Circle, Square, R2, L2. If you entered the code correctly, you will hear a sound. All weapons in free patrol mode and all bonus item menu options will be unlocked.

All Missions
At the main menu, press Down, Up, Left, Right, X, Triangle, Circle, Square

Bonuses:
Get a commendation on the indicated mission to unlock the corresponding bonus in free patrol or single player modes.

Ambulance in free patrol: Mission 10
APC in free patrol: Mission 14
Aqua theme: Mission 16
Bomb truck in free patrol: Mission 11
Bus in free patrol: Mission 8
Desert Eagle in free patrol: Mission 6
Flower power theme: Mission 3
Halloween theme: Mission 5
Low gravity: Mission 7
Machine gun in free patrol: Mission 15
News van in free patrol: Mission 12
Pizza truck in free patrol: Mission 19
Rear-wheel steering: Mission 2
Rocket launcher in free patrol: Mission 17
Shotgun in free patrol: Mission 4
Silly speech: Mission 13
Slow motion jumps: Mission 1
Tank in free patrol: Mission 20
Taxi in free patrol: Mission 9
Van in free patrol: Mission 18