All tracks:
Enter CHIMPGIVEAWAY at the cheat code screen.

All gadgets:
Enter GADGETCLEAROUT at the cheat code screen.

All cars:
Enter MONKEYSPOILERS at the cheat code screen.

Kid mode:
Enter THOSEWACKYKIDS at the cheat code screen.

Dastardly difficulty setting:
Enter FASTCARSAGOGO at the cheat code screen.