At the title screen, hold L + Z + C-Up + C-Down. If you entered the code correctly, the game will automatically go to the character selection screen. Press C-Left or C-Right to select a level. You will automatically begin with 99% invincibility. -From: dolph@boudros.com

Repeatedly roll against a wall until money appears.

The following objects may also be used as weapons:

Totally destroy a car, then Smasher can pick up the engine and use it as a weapon.
Destroy the airplane at the Airbase to use its gun.
Destroy the two large black structures found in the Hovercraft level to get a flare gun.
Destroy the police car in the Car Park level to get a rocket launcher.