All Boards:
At the title screen enter Circle, Circle, Square, Circle, Square, Square, Circle, R1
to unlock all Boards.

All Tracks:
At the title screen enter Left, Right, Left, Right, Circle, Circle, R1, Square
to unlock all Tracks.

All Sk8ters:
At the title screen enter Left, Left, Circle, Circle, L2, Square, Right, R2
to unlock all Sk8ters.