We have a toybox without a lid. Until recently, if it didn't all fit in the toybox, we purged until everything fit. We would do this whenever it started overflowing. It was helpful for all of us to remember that it has to fit inside the container or its clutter.
Then we were gifted with so many poofy princess dresses, there was no way more than even a couple could fit in the box. So I erected a garment rack over the toybox, and the poofy dresses hang on plastic hangers on the garment rack. I also put a stool nearby so the kids can reach the garment rack to put stuff away. But mine are 6 and 8, so they're old enough to do this.
I saw someone with dressup on a garment rack once and wanted to laugh hysterically. No way was I ever going to do THAT. Until it was the best clutter-free option, and then I ate my words.
One possibility, more little-kid-friendly, would be to put a series of hooks up on the wall and make sure all your dressups have a loop or even a hole that can be used for hanging them on the hooks.
I wouldn't sort stuff, though (as in ziplocks) because that would be too much work for me personally, and I like that all the costume pieces are mixed up to foster extra creative combinations.
- homeschooling mom to three teens and a preteen