Enter the following codes at the 'Title' screen to unlock the corresponding effect:

Unlock Classic Pitfall Game:
Hold L + R and press B, B, Left, Right, B, X, A, Up, B.

Unlock Original Pitfall Harry:
Hold L + R and press Y, Left, Down, X, B, Y, Y, Left.

Unlock Pitfall II: Lost Caverns:
Hold L + R and press Left, Right, Left, Right, Y, Y, Y.

Unlock Nicole
Hold L + R and press Left, Up, Down, Up, B, Up, Up.

Unlock Bottomless Canteen:
Hold L + R and press Left, X, B, Down, X, A, X, B.

Unlock Global Show Motion:
Hold L + R and press Y, X, Up, X, X, Up, B, X.

Unlock Hyper Punch Mode
Hold L + R and press Left, Right, B, Up, B, Right, Left.

Enter the following codes at the 'Title' screen.

Unlock Bottomless Canteen:
Hold L + R and press Left, X, B, Down, X, A, X, B

Unlock Global Show Motion:
Hold L + R and press Y, X, Up, X, X, Up, B, X

Unlock Hyper Punch Mode:
Hold L + R and press Left, Right, B, Up, B, Right, Left

Unlock Nicole as a Playable Character:
Hold L + R and press Left, Up, Down, Up, B, Up, Up

Unlock the Original Pitfall Harry as a Playable Character:
Hold L + R and press Y, Left, Down, X, B, Y, Y, Left

Unlock Classic Pitfall Game:
Hold L + R and press B, B, Left, Right, B, X, A, Up, B

Unlock Pitfall II: Lost Caverns:
Hold L + R and press Left, Right, Left, Right, Y, Y, Y

Play as Nicole
Hold L+R then hit LEFT, UP, DOWN, UP, B, UP, UP.

Bottomless canteen
Hold L+R then hit LEFT, X, B, DOWN, X, A, X, B.

Hyper Punch Mode
Hold L+R then hit LEFT, RIGHT, B, UP, B, RIGHT, LEFT.

Unlock original Pitfall
Hold L+R then hit B, B, LEFT, RIGHT, B, X, A, UP, B.