Flintstones

At the title screen press Up, Down, Up, Up, Down, Up, Right, A. Then press Start to start the game. Note: you will skip the main menu.

At the title screen, press Right, Left, Right, Left, Down, Down, Down, Up, Left, B. Your lives will go back to 9 when they run out.

At the title screen, hold A + B + C + Left and press Start. Use the directional pad to choose any of the six levels in this game.