Most everyone knows you can keep a hero's uniques, gear, and anything you've equipped to them in their own slot. And, of course, a hero's own costumes can go in their tab. You can also keep Ultimate Upgrade tokens for that specific hero in his / her tab. But, there are several other things you can do with a hero stash tab that not everyone is aware of.
The first and most well-known of these is the "any hero" uniques. You can put them into any hero stash while they're unbound. There are a few of these that don't work for EVERY hero. There's a cape that only works on heroes with capes, and a few that only work for "gun heroes".
You can put any unbound ring in any hero stash, as well as any unbound uru-forged items.
You can store unbound insignias in any stash tab for a hero that COULD equip that insignia. So, you can store SHIELD insigs in any hero stash tab, X-Men insigs can go in any X-Man or former X-Man, etc.
FYI, if you bought ONLY the Ms. Marvel and Luke Cage hero stashes, you could store every team insig currently in-game in one or the other. Between the two of them, they've been on every team currently in-game.
Oh, one more. If you have a hero stash for a hero you don't use often, let's say X-23, and you have some artifacts you need to store, you can bind them to her, store them there, and unbind them when you really need them. This works REALLY great with visuals, as you don't even need to bother unbinding them. Just use them up on whatever hero you want, and the crafter won't care who they were bound to. My X-23 has her whole stash full of shrinking / growth artifacts for whoever needs one later.
I hope this has been helpful to someone. I've parsed this information out before, and wanted to toss it up in hopes new people will see it and make good use of their stash, as space is a premium in this game.
Thanks, @Krodmandoon for pointing out that you can store any Starktech in any hero stash reguardless of who it's for. I was sure I'd forget SOMETHING. I went back and added the line about costumes, but totally forgot about Starktech, even though I put them in my hero stash myself.
