Collect 11 bonus stunt items in Challenge 8.

All Gadgets

Hit 25 barrels in Challenge 7.

All Worlds

Find the Hidden Key in Challenge 18.  Look in the Mines near the end of a tunnel.

Unlimited Ammo

Hit 50 barrels in Challenge 18.

Unlimited Health

Hit 179 barrels in Challenge 17.

Unlimited Turbo

Collect 8 Zappers in Challenge 4.