Roadkill cheats and cheat codes for Gamecube

Cheat Codes:
Pause the game play and highlight the "Map" option. Then, press the 
following button cheats. The sound of an engine will confirm, 
if the typed codes are accepted.

Effect - Code 
Decrease RIOT level - Y, X, A, B, Y, X, A, B, Down 
Extra money - Y, X, Y, X, B, A, B, A, Down, Up 
Increase RIOT level - Y, X, A, B, Y, X, A, B, Up 
Infinite ammunition - Y, B, B, X, Y, B, B, X 
Powerups respawn immediately - Y, A, A, Y, B, X, X, B, A, B, X, Y 
Restore health - B, X, B, X, B, X, B, X 
Tornado - Y, X, A, B, B, A, X, Y
Unlock all Vehicles - Up, Down, Up, Down, Y, A, Y, A, B, X, X, B 

Pop a wheelie:
Find a short hill then hold Down and jump it.