During gameplay press and keep held L1+L2 then enter the following combinations for these different effects. The screen should flash blue if it has worked

Infinite Health
Down, Square, Triangle, Down, Square, Triangle, Circle, X, R2, Up, Select

Infinite Ammo
Down, Square, Triangle, Down, Square, Triangle, Circle, X, R2, Right, Select

Infinite Lives
Down, Square, Triangle, Down, Square, Triangle, Circle, X, R2, Down, Select

Infinite Charge
Down, Square, Triangle, Down, Square, Triangle, Circle, X, R2, Left, Select

Immortality
Down, Square, Triangle, Down, Square, Triangle, Circle, X, R2, Triangle, Select.

Unlock All Extras
Down, Square, Triangle, Down, Square, Triangle, Circle, X, R2, Circle, Select.