Go to the main menu and hold L1+R1 and press up circle down square up up down down.

the other codes are key sesitive so be careful

Inf. Health- 8wonder
all levels- KKstory
Inf. spears- lance 1nf
pistol- KKtigun
sinper- sn1per
all bonuses- KKmuseum
999ammo- KK 999 mun
tommy gun- KKcapone