While in level 1, go to Gloria's Pad, and kick open the left gate. Destroy the hay barrels in the Penguins' Pool then go back to Gloria's Pad. Look through the left gate and the hay barrels will be there. Go back to the Penguins' Pool and they will be gone.
Banquet
Goto the main lemur that is on the drum where all the food lies. Talk to him 10 times in a row to earn food. This can only be done 2 times.
Flying Bird Mini-game
When you are in level 3, go into the right subway entrance to find one of the arcade games.
Invincibility
While playing a game, press Up, Down, A(2), R, L, Black, White, Y, X, B.
Level select
While playing a game, press R(2), B, White, L, A, Y, R, Y.
Power Ups
While playing, pause the game. Press B, A, A, B, Y, L, X, R, L.
Appearing and disappearing hay...