I don't know, just apologize to him? Offer to take him to the dollar store to find a new bear? Ask him to help you pack so you don't accidentally toss anything he wants? (I think at that age I would try to involve him in the decluttering of his stuff. It's such a luxury right now to be able to declutter my 19mo's stuff on my own, since he doesn't notice yet!)
I have some things I'm on the fence on whether to keep or toss. I usually put things like that in a box in the basement & then if I don't miss it after a few weeks I sell/donate/toss it.
Anyway if he doesn't mention it again I'd let it slide but try to have some mental plan in place in case he brings it up!
ETA: You could make a box of the things you plan to donate & explain to him that you're giving these things to other kids, but he should look through it, & if he wants to he can keep one or two items from the box.
Co-sleeping is really wonderful when your child actually SLEEPS!!