Going through the same thing. I am getting better at dealing with, but still need to improve.

There is a lady at work who I pass things onto, small clothes, some toy sets etc. I feel better knowing that I am passing it on to someone who will appreciate it.
I still do donate to Charity OP shops. I used to get all worked up about the "what ifs". What if someone bought it for $1 and sold it for $20? That type of thing, but then I realised after talking to a close friend that relies heavily on OP shops, that often it is people like her that will pick up the item and really appreciate it. So that makes me feel better about it al.

Like Kim, these days we try to stick to adding to existing collections in order to stem the tide of stuff.