Kingdom Hearts seems to have a lot of useless rooms in my time of playing it, but I also haven't played too much of it lol.

I think a couple of Metal Gear Solid games are guilty of the same thing, but I can't think of any game that I've played that has useless items specifically.

list some useless things in games ok i will,
First up is the oh (my god) "powerup" in parodius. It makes you lose all your power ups and its existance is to add risk to the rulette and to make your life a nightmare.
Next up is the rock option in pokemon r/b/g, all this did was make you through a tiny rock at the pokemon and tick it off. At least the bait makes them less likely to run and while im on the subject of useless, this item requires a gameshark to get. its called the gs ball and what does this mysterious ball do? Nothing, absoulutely nothing!
My next item on this docket has probbly happened to a few players here. It was aleged to have been put in to punish cheaters, however thanks to glitches in certain pokemon games or just plain bad luck you could get a destructive bad egg. this lovely egg has a plethora of effcts and none of theme are good, the most common one is a neverending hatch sequince, way to go nentendo at least test some thing like that before you try it next time. Finaly on this growing list is a lovely item from dokapon kingdom, you can only get this lovely item from webber and it's super awesome! What does this mystery item do? Why simple, it destroys your other items! Yup thats right this is the big bug im talking about and its worse if your an alchemist, as you tend to keep it longer due item cloning.
The final thing on this list comes from a game series called robopon, In one of the games you could get mushrooms which have a wide list of spirits they could summon. Amoung them are some duds but the worse of these duds is a grim reaper lookalike that just makes invintory and your hard earned cash disapear, like a bad magic act. He has some other effects but when he shows up its better to reload trust me he does go away after so meny battles but heres the thing the amount needed to get him to leave is random and just to troll he never will tell you how many, at least he looks cool any way this list has gone on long enough i sould let the other users post stuff too dang my hands and head hurt now.

On disk DLC. That honestly gets me so mad. You have the content already on the disk but you have to pay to unlock that content. I'm looking at you destiny. 

From Pokemon: Sunflora, Sunkern, and Luvdisc. Also as far as items go, Iron Ball. Nobody uses fling anymore, so that item is therefore uselsess.

From Mario: Fake Item Box. Nobody falls for it (except for some CPU), and holding it behind you won't protect you from a red shell, so it's completely useless.

I remember one ralts. Which no one has said, but when you first obtain this pokemon. You get excited then you see it only has growl.....like only growl and no other move. To get confusion you have to grind this pokemon to level 5 if I can remember. Please correct me if I am wrong about that, I love ralts when I first played a certain pokemon game to get one. To me it was a big disappointment, and I find it useless.... that move I mean it only helps lower attack moves that's it. I'm not going to list some other stuff down since some people already have.