I think a lot of you are saying how useless some of these items are and you don't realize that they actually are used in more than just one location.
The Spinner from Twilight Princess is used outside of Arbiter's Grounds...it's used in Hyrule Castle, City in the Sky, Temple of Time, and even in Hyrule Field a little. It's just used in Arbiter's Grounds more than anywhere else. I also believe that there is a rusty switch in the Spirit Temple for the Megaton Hammer, and in the Shadow part of Ganon's Castle as well.
For me, a very useless item would have to be the Giant's Knife. Like some of you have said, it is completely optional and breaks quickly.
The Dominion Rod. It is used as part of the story and to get some heart pieces, but besides that, it's completely useless! The Spinner, the Ball and Chain, the Hammer, the Sand Wand, all of them can be used as weapons, but the Dominon Rod can't!!!