Unlimited ammunition:
Intentionally hit 50 Barrels while completing Challenge 18.

Unlimited health:
Intentionally hit 179 Barrels while completing Challenge 17.

Unlimited turbo:
Collect 8 Zappers while completing Challenge 4.

Timer speed:
Intentionally hit 13 Detour Signs while completing Challenge 15.

All cars:
Collect 11 Bonus Stunt items while completing Challenge 8. Note: The Bonus Stunt Items are the purple balls with silver rings rotating around them.

All worlds:
Find the Hidden Key while completing Challenge 18. The yellow key is in the Mines, across a trestle at the end of a tunnel.

All gadgets:
Intentionally hit 25 Barrels while completing Challenge 7.

Laser upgrade:
Note: You must get an "A+" rank when doing the following. Complete all challenges, then unlock the "Timer Speed" cheat. Set it to 10% speed. Change the difficulty level to very hard then complete Challenge 18. Get the "A+" rank to unlock the "Laser Upgrade" cheat.