On the one or two player select screen, type "SPICY BEANBURGER". The guy should then jump up and down. During play, but not on the map screen, press '=' to add guys. Press 'ENTER' on the keypad to get a card. On another version type "KID" on the player select screen and use the same keys.
When you get to the bonus room, if you fall down to the exit, then press fire, it will open. While it's open press 'P', and you should be given an other go at the bonus room.