I know we all got one. That one item, utterly useless by now, that we just hold on to forever because we like it regardless.
Another topic just reminded me of this, but it seems like a lighthearted thing to post on instead of yet another trollpost.
Mine’s the Netherwing Ledge Booterang, great flavor item, first WoW item that made me laugh and my Azure Netherdrake was my first really big in-game get.
EDIT: And yes, that means I’ve had that daily in my Quest log since BC
Stratholme Holy Water
Because you never know when you might need it.
I have too many, because I’m a pack rat. 
But my favorite is this:
The Pet Rock. It Looks Happy. 
You’re not a true rogue if you don’t have these.
Oh, do you get to keep these glasses after hand in? I’ve never handed the quest in because I didn’t want to lose them! (on my Rogue.)
Thank you!
You have to sell them to a vendor first then after turn in you can just buy it back.
I keep the four Pandaria weather stones on me at all times.
I very rarely use them, they still have most of their charges because I’m afraid of running out. But I don’t know. They’re neat toys and look cool together as an item set. That’s my whole reasoning. I’m weirdly attached.
I’ve had them in my active bags for over seven years now. I won’t even bank them.
The Drustvar resurrection stone thingy. Never used it once but it’s in my main backpack.
I feel that, I still have scourgestones and all sorts of weird junk hanging around, but that Boot, that stays in the bag 
My Warlock still has the Dreadstead summoning stones for the quest to get the Dreadsteed mount.
My Priest has benediction staff.
Barov Servant Caller and a few other removed items like this. Not sure why. They’ve been sitting in my bank for years and years.
QoL Changes that Mattered
I did that and the Paladin Epic mount chain before they dumped then and… whew… don’t miss that.
Wasn’t that Barov Peasant Caller?
Nope! I linked it :o
BPC was the Vanilla version, there’s my confusion
I cant link for some reason, but its on wowhead
Oooh! Okay yeah I started in wrath :>
I think I have a thing for odd trinkets with weird procs/use effects. I may have gotten rid of the servant caller D:
That’s not my certificate of thievery.
Haunted memento from my first account. The only thing left of it. The circumstances behind my friend getting it and being able to pass it on were very well timed.
I have a few items in my DK’s bank that I couldn’t bring myself to trash. Some holiday clothing, the Wrath-era Brewfest trinket that summons the brew lady, Deathbringer’s Will, that I got when it was current (and it was AWESOME), Shadow’s Edge (never got Shadowmourne 
), the bow from Karazhan, and various other mementos.
He was my main for years, so I accumulated some neat stuff.
Unidentified plant parts
(not joking)