Secret Cave In Whoopie World
In Whoopie World go to where Paint Misbehavin' is and jump off right next to the edge and hold B. You should hook on to a ball with your tractor beam, then jump into to the cave next to it for a ticket.

Secret Entrance in Clowny Island
Go into the dunes and once you go down the ramp go right. You'll find a stick with bees on it. Go in it.

All vehicles
While playing, pause the game and hit Up, Down, Z, R, Left, Up, Down, Left, and then Down twice.