These items can be used one at a time. Some of them consume magic points (MP) when used.
By using Magic Powder on a shrine next to the blacksmith's house, a strange bat-like creature appears and "curses" Link, resulting in a doubled Magic Meter. The one-half means that magic is drained at one-half the normal rate.
The Shovel is needed to find the Flute. In the Game Boy Advance version you get to keep it after finding the Flute, and it can then be used to dig up Rupees. In all other versions the Flute replaces it in the items screen.
The Hookshot allows you to shoot a grappling hook that attaches to certain kinds of walls and objects; when the chain retracts, Link gets pulled along. It is useful for clearing pits and reaching other hard-to-access places. Like the Boomerang, the Hookshot is useful for stunning and killing enemies, and collecting items from afar.
Bombs damage enemies and open new paths…but don't get too close! You can carry more bombs by visiting the Fountain of Happiness