Pause the game and hold R1 and L1 then press Down, Up, Right, Left, Down, Up, Square. You will hear a sound if entered correctly.
All Store Items:
At the main map enter L1, R1, L1, R1, R2, R2, Triangle.
In the character customization screen, highlight the name option and enter L1, R2, R1, L2, L1, R2, R1, L2, Square. Left and right will select your character. Code must be entered quickly.