Cruis'n USA cheats and cheat codes for Nintendo 64

Unlock Golden Gate Park track
Hold L + C-Left + C-Down at the track selection screen.

Unlock San Francisco track
Hold L + C-Right + C-Down at the track selection screen.

Indiana track
Hold L + C-Right + C-Up at the track selection screen.

Bonus vehicles - All Terrain Vehicle, School Bus and Police Car:
Hold C-Up + C-Left + C-Down at the car selection screen.