When Collectors Move

I am now facing the onerous task of transporting all my possessions to another home. Like most collectors, a large percentage of things I have collected fall into the category of "why did I buy that?". Since I am down sizing to an even smaller home,these things now need to be disposed of--the good, the bad, and the ugly alike. My attic is so cluttered that I can't step one foot from the stair well. Where and how to start? I can use the excuse that I've been using that's it's too cold to work in the attic and wait until it's too hot to work there. The only good thing about moving is that now at least my son will have to finally have to remove his stuff. That will almost make the move worthwhile.