All items
At the Press Start screen, hold L + R and press Left, Left, Down, Right, Right, Up, Left.
Everyone invincible
At the Press Start screen, hold L + R and press Left, Down, Down, Right, Right, Left, Down.
Level select
At the Press Start screen, hold L + R and press Left, Left, Right, Down, Down, Up, Right.
All characters' jet packs
At the Press Start screen, hold L + R and press Left, Up, Right, Down, Left, Left, Up.