Donkey Kong Country - 50 Extra Lives

Blast through mine cart carnage:
Near the begining jump over the cannon and fall next to the wall underneath. You should get blasted out of a cannon and sent in a cart almost all the way to the end of the level.

Infinite Bananas:
In Bouncy Bonanza, after you obtain the frog, you will continuously be brought down this small path. If you jump up, you will get three bananas. Now, enter the cave where you got the frog, and you will fall down again. The same three bananas are there That means you can do this forever and you will get infinite bananas.

Jump in mid-air:
This works in the stage, "Mine Cart Carnage". Hit the Star Barrel in the level, and then either die or pause and press "Select". Enter the stage again. When the Star Barrel explodes, press Y and B simultaneously. You should now be jumping in the air, keep jumping by pressing Y and B in succession. You can use this glitch to jump all the way to the end of the stage.