Gerudo Token

This key item in The Legend of Zelda: Ocarina of Time allows Link to pass through Gerudo Fortress without being thrown in prison. Link obtains this from Naburoo's 2nd in Command after sneaking past all of the Gerudo Gaurds and freeing the 4 carpenters, Sabooru, Shiru, Jiro and Itchiro. This is vital when journeying to the Spirit Temple for the first time, as you need the card to have the gate opened without being caught, as well as being able to walk around freely and being able to participate in the horse challenge and training grounds.

Trivia
When Nabooru's second in command gives link the Gerudo Membership Card her clothes correspond to the color of Link's tunic.