Infinite Fairy Tears

After you defeat every level of the Cave of Ordeals, you can go to one of the ancient spirits (in any of the springs with fairies in them) and talk to them, they'll take you back to the Great Fairy and she'll fill an empty bottle with Great Fairy's Tears. She'll keep doing this aslong as you have an empty bottle. She'll warp you out of the cave after she fills it.