Here is a link with a ton of info on the game with cheats/secrets. IGN: Banjo-Kazooie Cheats, Codes and Cheat Codes

Also, specific info on the ice key...

"Glitch: Ice Key Trick
Here is a way to get the ice key without using any cheats or Gameshark codes. Get the orange jinjo in Wuzza's cave, right in front of the ice key. Next, face away from the ice key. Perform a backflip, and if you did it right, you will fall into a hole in the wall, allowing you to reach the key. (Note: The game might freeze if you grab the ice key.)
Submitted by super surge"

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