Truck:
Select any car, then hold L1 until the race begins.

Buggy:
Select any car, then hold R1 until the race begins.

Various cars:
Select any car, then press Down at the transmission selection screen to cycle
between a low rider, bus, rocket engine car, taxi, and police car. Note: The
number of cars that are selectable will vary depending on how much of circuit
mode has been completed. To drive the police car, circuit mode must be
completed.

Hidden car:
Select any car, then hold R1 + R2 until the race begins.

UFO:
Hold R1 + R2 + L1 + L2 at the car selection screen and choose a car. Keep those
buttons held and press X at the transmission selection screen. Then, hold
Triangle until the race begins.

Reversed tracks:
Complete circuit mode to unlock an option for forward and reversed tracks.

Stunt mode:
Complete tournament mode to access a stunt mode option on the Golden Gate track