I know I'm new here, but I just wanted to offer my sympathies - I had something very similar happen to me in a previous relationship where he "kept" a substantial portion of my wardrobe, including everything that was "slutty" - this was a minor financial setback at the time as it was going into summer. I must admit I didn't turn the other cheek - I "lost" a couple items that had a lot of sentimental value to him to get even.

Okay so I do have a point here and it's that these things can often get really ugly, as I'm sure you know. Perhaps it was petty of him, or selfish, or anything else - it may be true; I don't know the situation and I won't try to insult someone I've never talked to. But most people here are right in that you're probably better off now, especially in the long run.

I found it emotionally helpful to try to remember the good times about the relationship, the times before the break up that made you happy and brought you joy - remaining compassionate and understanding that these actions very likely are coming from a place of hurting, insecurity, and lashing out. It's hard to do, but it makes you feel a lot better than dwelling on how much he has hurt you. (I'm NOT saying these feelngs aren't valid or you shouldn't let yourself experience them, merely cautioning against dwelling on it)

A thought I had when you said you wonder what he'll do with them - he very well might put them in a box somewhere and bring them out occasionally and cry over them, or something similar. (I found out for a fact this is what my ex did with the stuff he "kept")

I hope something I've said might help you and even if not ... know these words are coming from someone who, even if her advice is wrong, feels very badly for the difficulties you're going through and hopes things will work out for you.