Unlimited Ammo
     To get unlimited ammo, hit 50 Barrels during Challenge 18.

Unlimited Health
     To get unlimited health, hit 179 barrels during Challenge 17.

Unlimited Turbo
     To get unlimited turbo, grab eight Zappers during Challenge 4.

Unlock All Cars
     To  unlock  all  cars,  hit 11 Bonus Stunt items while completing
Challenge 8.

Unlock All Items
     To unlock all Items, hit 30 Barrels during Challenge 7.

Unlock All Worlds
     To unlock all worlds, find the Hidden Key in Challenge 18.

Upgrade Your Laser
     To upgrade the laser, finish Challenge 18 on very hard difficulty.