There are a lot of cheats/glitches in SM64, but one of my favorites happens in 
Shifting Sand Land (the desert level). For this glitch, you must be able to use 
the Wing Cap and cannons on this level. First, when you start the level, go directly 
to the corner of the stage (there will be a cannon and a wing cap box). Then you get 
the Wing Cap and QUICKLY go in the cannon. Aim the cannon very high and to the left, 
when you launch, you will hit a wall and fall back into the cannon, taking a half 
of your full health. Repeat the cannon aiming/firing and you will notice that you 
will have no health at all once you go back in the cannon. Finally (if you still have 
the wing cap), launch anywhere! You will be flying with no health! If you grab a coin 
while flying, you do not heal. Also you go straight through stars. Once you land, 
Mario will die. Try it! I have done this a million times, and I guarentee this will work!