Bueno Nacho costume:
Have the Game Boy Advance game Kim Possible: Revenge Of Monkey Fist in the cartridge slot.

Commando costume:
Have the Game Boy Advance game Kim Possible 2: Drakken's Demise in the cartridge slot.

Super Suit costume:
Have the Game Boy Advance game Kim Possible 3: Team Possible in the cartridge slot.

Unlimited lives:
Hold L + R and press Y, Y, Y, X

99 lives:
Hold L + R and press A, A, A, Y, X, Y, B, A

Extra life:
Hold L + R and press A, A, A, Y, X, Y

Full health:
Hold L + R and press A, A, A, Y

All gadgets:
Hold L + R and press Y, Y, X, B, A, Y, Y, A

All costumes:
Hold L + R and press B, A, X, Y, A, B

9,999 credits:
Hold L + R and press Y, Y, X, B, A, Y

Invincibility:
Hold L + R and press Y, Y, Y, X, A, B

Level select:
Hold L + R and press X, Y, X, A, X, B