Stop N Swop is probably one of the biggest, and most interesting secrets in Banjo-Kazooie. For those who don't know, it was a cut feature from the Banjo-Kazooie series. The basic way it was supposed to work was to allow the player to swap Banjo-Kazooie and Banjo-Tooie by taking one game out of the N64 and putting the other in. Thus allowing the player to transfer data between games and unlock secrets. It was dropped because doing this could damage the Nintendo 64, therefore Nintendo did not like the idea, and it was probably just a bad idea in the first place. It first began in the 100% cut-scene at the end of Banjo-Kazooie where Mumbo shows banjo getting the secret items, which are the two eggs, and the ice key.
Now for a while, many people believed these items could not be obtainable in Banjo-Kazooie, but they can be. They are obtainable by putting in codes via sandcastle.

The Ice Key



The Ice Key in Freezeezy Peak is obtained by putting in the code----NOW YOU CAN SEE A NICE ICE KEY WHICH YOU CAN HAVE FOR FREE----into the sandcastle in Treasure Trove Cove.

The Pink Egg




The Pink Egg in Treasure Trove Cove is obtained by putting in the code----OUT OF THE SEA IT RISES TO REVEAL MORE SECRET PRIZES----into the sandcastle.

The Blue Egg




The Blue Egg in Gobi's valley is obtained by putting in the code----A DESSERT DOOR OPENS WIDE ANCIENT SECRETS WAIT INSIDE----into the sandcastle.

The Cyan Egg




The Cyan Egg in Mad Monster Mansion is obtained by putting in the code----DONT YOU GO AND TELL HER ABOUT THE SECRET IN HER CELLAR----into the sandcastle.

The Green Egg


The Green Egg in Mad Monster Mansion is obtained by putting in the code----AMIDST THE HAUNTED GLOOM A SECRET IN HER BATHROOM----into the sandcastle.

The Red Egg


The Red Egg in Rusty Bucket Bay can be obtained by putting in the code----THIS SECRET YOULL BE GRABBIN IN THE CAPTAINS CABIN----into the sandcastle.

The Yellow Egg


The Yellow Egg in Click Clock Wood can be obtained by putting in the code----NOW BANJO WILL BE ABLE TO SEE IT ON NABNUTS TABLE----into the sandcastle.

Courtesy of Kafei2006

In order for these codes to work, you first must spell out CHEAT in the sandcastle. You should hear a moo sound after each letter. You will not hear the sound when putting in the actual code. Once you collect the items they will be stored in a menu entitled Stop 'N' Swop, under the View Totals section of the start menu.

Stop n Swop Menu

Once you put in these codes and collect the items, you will have them forever. The SnS menu will always be viewable in the game, erasing your game does nothing. Here is an explanation for why the game does this. Stop n Swop involved swapping the game carts to transfer the Stop n Swop items, and unlock secrets. So the game recognizes that you have the items, and keeps them, because in reality the game is still waiting for the items to be swapped from Banjo-Kazooie to Banjo-Tooie. Once you swapped the item, it would have probably disappeared from the menu until every item was swapped, then the menu would disappear altogether. Which means the game is still waiting for the items to be swapped, but they can't be due to the fact that the feature was dropped from Banjo-Tooie. This theory was first put up by Grey Jinjo in a post from The Rare Witch Project forums. This may or may not be the reason why the items are always viewable.

Well since this feature was dropped, obviously you couldn't use these items in Banjo-Tooie. So what did Rare do? Since they did promise these items would be in Banjo-Tooie, they did put them in, but in a very cheap way. You collect two eggs in Banjo-Tooie by breaking little plastic Banjo-Kazooie cartridges. The eggs unlock little moves, and other things in multi-player. You also collect an ice key which opens a safe to a mega glowbo. Sadly there was no way to Swap the cartridges or collect the items in Banjo-Kazooie from Banjo-Tooie. Upon learning this, left a lot of people disappointed...

Rare has made references to Stop n Swop in other games just to taunt and tease the fans. Some games include Grabbed by the Ghoulies, when you enter the classroom and look at the chalkboard, it shows how to "activate" Stop N Swop.(Which obviously doesn't work).

Their is also a reference in Banjo Pilot where you can purchase an item called Stop n Swop.

In an interview Rare has stated that they want to put a special ten year anniversary reference to Stop n Swop in Banjo Kazooie 3. They might finally tell us exactly how it was supposed to work.