So often, the reason clean-out-and-declutter sessions hit a dead end isn't lack of motivation, but an object you can't quite say you'll never need again—an arcane instruction manual, computer games you might just play again, a baking dish you'll need for a theoretical cake. J.D. at the Get Rich Slowly blog hit upon a great idea for worry-free selling and tossing while reading one of his favourite books, Your Money or Your Life:
Rather than keep the stuff you aren't using, you sell it to somebody who will use it, and then stash the proceeds for future use. It's sort of like "Stuff insurance".
In other words, you put the money you earn from selling off your quasi-useful stuff in a separate, interest-earning account, and use it only if you need to buy something again. It's a perfect "sub-account" for those who can create individual funds in their online bank, and a good way to trick yourself into responsible saving.