Deku Nut Upgrade 2
At the start of Ocarina of time you are able to carry up to 20 Deku Nuts. They are useful for stuning enemies so that you can attack. In order to get the second Deku Nut upgrade, you must go to the Lost Woods. Right outside the entrance to the Sacred Forest Meadow there is a rock. Place a bomb next to it and, when it blows up, go down the hole.
Down the hole is a Secret Grotto containing two Business Scrubs. Bounce back the nuts they launch and then go speak to the first one. He tells you that for 40 Rupees he will help you to carry more Deku Nuts. Pay him the 40 Rupees, and receive the second and final Deku Nut Upgrade.