B.C. Kid

Select 'OPTIONS' from the title screen.  
On the option screen, use and enter the following sequence:

UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT

Now start the game and infinite lives are yours.

Jump up and turn on the autofire on your joystick.  You'll glide
through the air while spinning madly.  This should help you dodge all
the dinosaurs and valcanoes.