Bonus Cars:

For some secret cars, hold CU, CL, and CD at the Car Selection screen.

Bonus Tracks:

Go to track selection screen and press the following buttons:

Golden Gate Park: CL, CD, L button

Indiana: CU, CR, L button

San Francisco: CR, CD, L button

For Faster Different Colored Cars:

You must win "Cruise The USA" and win. Each difficulty level earns you another car.