Level select:
Press Up, 2, Down, 2, 2, Left, 2, 2, 2 at the title screen.

Destroy other cars:
Drive to the top left corner of the first breakfast table and press 1 + 2.

Unlimited lives:
Jump off the bottom left corner of the first breakfast table.

Slow opponents:
Drive off the top right hand corner of the first breakfast table in reverse.

Better traction:
Stop on the milk on the first breakfast table and press Up + 1 + 2.

Super slides:
Stop on the syrup at the middle of the first breakfast table and press 1 + 2.

Turbo mode:
Cross the finish line of the first boat race in first place and in reverse.

Squinky Tennis mini-game:
Note: This trick requires two linked Game Gears. Hold Start and power on the Game Gear.