Top 5 of useless items.
5.: The bait from The Legend of Zelda (NES), representative for all of the items that are needed at exactly one point in the respective game.
4.: The golden feathers from Wind Waker, representative for the collectibles, be it here or in the DS games.
3.: The Deku nuts in Ocarina of Time. I'd rather throw a bomb. And when I want to stun enemies, I use the boomerang.
2.: Circus Leader's Mask, representative for most of the non-transforming masks. Tons of masks are rather useless (how about the rabbit ears - in Ocarina of Time?), but the Circus Leader's Mask takes the cake. Majora16 said it all on page 2. Its only purpose (besides getting the Fierce Deity Mask) is to make it easier to get the Romani Mask, which you already have once you get the Circus Leader's Mask.
1.: The telescope from Wind Waker. Not only is it only needed to trigger one video sequence, it actually becomes redundant after you get the pictobox, and still hogs the top spot in your inventory. And it's not even yours!