LOL!! Although this isn't a code, the single most useless thing ever in a game is the reward for getting all the Gold Skultullas in Zelda 64. By the time you're that far into the game, you don't need rupees anymore!

"Once upon a midnight clear...Saw the world through eyes of a seer...
Through the crystal lens I foretold...The past, the future, and present unfold."