All cars
Collect 11 Bonus Stunt items while completing Challenge 8.
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 whendoing 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.
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.