Unlockable Weapons:
Rocket Launcher: 
To the left of your start position in "Bank Standoff". 
Crossbow: 
In the middle of the map on "Chinatown Showdown" 
Baseball Bat: 
Back of the room in "Bum Encounter," near the refrigerator.

Snoop Dogg:
Collect 30 doggy bones that are scattered throughout the streets. (remember the license plate!)

Bonus FMV Ending:
Complete the game with all three endings.

Change Player Skin:
Once unlocked you must create a saved game with the correct license plate name to play as the unlocked character:
Enter these codes as your license plate at the start of the game:
M1K3 Play as commando 
HAWG Play as biker 
TFAN Play as gangster 
B00B Play as female punk 
JASS Play as donkey  
TATS Play as tatooed lady 
PHAM Play as butcher  
MNKY Play as male punk 
BRUZ Play as boxer 
J1MM Play as corpse 
FATT Play as police officer 
P1MP Play as pimp 
MRFU Play as asian  
5WAT Play as S.W.A.T.  
B00Z Play as street bum 
PIMP Play as pimp 
B1G1 Play as your boss 
ROSA Play as your partner 
HARA Play as asian worker 
FUZZ Play as Officer Johnson 
HURT_M3 Play as your partner in underwear
ACTVZZL Play as Snoop Dogg (You need 30 bones too!)
NOMAYO Play as Sandwich Guy
DOGTAGS Play as Soldier
AWYEAH Play as Afro Guy
THUGLYF Play as Officer Dick