Sounds like a typical BPD tactic.
He knows this is burdening you and knows it also keeps the two of you connected, if he doesn't take responsibility to come get his things.
What person in their right mind would actually risk having their items thrown out like you claimed you would do. My guess is that he knows you really wouldn't do it. So he's playing games and manipulating you. Don't give him that power any more. Stop being too nice. He doesn't deserve it. This is a time stick up for you and he no longer deserves your energy.
I would consider really being done. Can you have someone help put his items outside in the yard or whatever front area you may have? Tell him on "this date" the items would be outside. He can arrange to come get them and if he doesn't, a sign goes up that says "Free to anyone who wants this" and you can have the public come sort through and take what they want.
You've been way fair and have truly gone above and beyond to be accommodating to coordinate the pick up. No more. He's using this as a way to keep you strung along.
It's kind of like the motto "bad press is better than no press"... well, your ex is using this as the last shred of contact and connection to manipulate. I know the pattern all too well. Time to be DONE with him! You can do it.