To unlock the secret functions, go to the map screen, hold L+R and enter one of the following codes:
Double damage: A, A, X, A, A, A
$ Million: X, X, Y, X, Y, X
Super Cop: Y, A, Y, A, Y, Y
Ultra easy mode: B, X, A, A, Y, B
Unlimited Ammo: B, X, A, X, X, Y
Unlimited Endurance: B, X, A, X, A, B
Music Tracks: B, X, B, X
Fights Open: X, X, B, B, X
Street Races Open: Y, Y, A, A, Y
Puma Costume: Y, A, B, X
Redman Gone Wild Mini-game: Y, A, A, X, A, X
Zombie mode: B, Y , X, A, X, A