A few words on that ice key and those colored eggs...

Rareware is notorious for building game levels that allow the player to see an ultra-cool awesomely neato bonus that is tantalizingly out of reach. The platform upon with the item rests is just a little too high to jump to or is blocked by a wall of ice, or some other such frustrating madness. In Banjo-Kazooie Rare placed an ice key behind a sheet of ice in Freezeezy Peak inside the walrus's cave and hid several colored eggs (although nobody knew that at the time) in several key locations. The game also featured a number of places that were inaccessbile, such as the mythical Sharkfood Island in Treasure Trove Cove that could supposedly be raised to reveal a secret cave, a locked door in Gobi's Valley, and a wine cask in Mad Monster Mansion that could not be shattered. Gamers spent months and even years trying to access these hidden areas. Plus, the ending of the game teased players further by showing these hidden areas unlocked, but were supposedly being saved for the sequel.

In 1999 the mystery began to unravel. Clever players using GameShark cheating devices were able to propel Banjo over the wall that kept the ice key out of reach and actually collect it. The game then triggered a secret mode called Stop 'n Swop in which the game told the player to, simply, stop and swap. But stop and swap what? And how? Rare remained silent on the matter except for revealing that somehow the key could be taken from Banjo-Kazooie and used in the sequel, Banjo-Tooie.

Banjo-Tooie was released in 2000 and before long gamers were dismayed to learn that Stop 'n Swop had seemingly been abandoned. The ice key and colored eggs were "taken" from B-K by finding bouncing game paks in the game itself and smashing them open, upon which the ice key and two colored eggs popped out. However, the sequel continued to hint and tease at the prospect of unlocking those hidden secrets in the original game. For example, a poster on the wall of a tavern shows Sharkfood Island raised. More background information on this is better left to the Banjo-Tooie node.

But back to Banjo-Kazooie... with the Stop 'n Swop shut out, GameSharkers again began to dig deep into the game and discovered a series of secret codes that, when entered on the sandcastle floor in Treasure Trove Cove, would unlock all the secrets revealing the ice key and seven, count 'em, seven colored eggs. For the record, the codes are...

  • CHEATADESERTDOOROPENSWIDEANCIENTSECRETSWAITINSIDE - this code unlocks Gobi's Door in Gobi's Valley
  • CHEATAMIDSTTHEHAUNTEDGLOOMASECRETINTHEBATHROOM - this code places an egg in the toilet in Mad Monster Mansion
  • CHEATOUTOFTHESEAITRISESTOREVEALMORESECRETPRIZES - this code will raise Sharkfood Island
  • CHEATTHISSECRETYOULLBEGRABBININTHECAPTAINSCABIN - this code places an egg in the captain's cabin in Rusty Bucket Bay
  • CHEATNOWBANJOWILLBEABLETOSEEITONNABNUTSTABLE - this code places an egg on Nabnuts the Squirrel's table in Click Clock Wood
  • CHEATDONTYOUGOANDTELLHERABOUTTHESECRETINTHECELLAR - this code smashes the wine cask in Mad Monster Mansion, revealing an egg.
  • CHEATNOWYOUCANSEEANICEICEKEYWHICHYOUCANHAVEFORFREE - this code shatters the ice wall in Freezeezy Peak, allowing access to the ice key

Collecting these items places them in your inventory, but with Stop 'n Swop abandoned there is no known way to transfer them to Banjo-Tooie. Exactly what these eggs would have done is unknown. Only Rareware knows for sure, and they ain't talkin'.


References:
http://www.rarenet.com
http://www.GameFAQs.com