While playing a game, hold R1 and press Left(2), Square, Circle, R2, Right, Triangle, L2. If you entered the code correctly, you will hear a sound. Then, pause the game and move to the bottom of the options menu to find the cheat selection.
Search underwater to the left of the base on the Medieval level to find a 3x Cargo Hold.
Crash into the church on the Medieval level at high speed to find a power-up.