Letter

In LoZ, Link is given the Letter by the old man in the north east part of Hyrule. When he shows the Letter to old women throughout Hyrule, they sell him Life Potions and 2nd Potions.

Also found in The Wind Waker, letters are carried in the Delivery Bag (although curiously they cannot be posted, despite the presence of Postboxes on most islands on the Great Sea).