I (finally) just gave myself permission to (re) purchase that item if in the future I found I needed or wanted it. Especially when money is tight, it's hard to do, but it was so freeing when I allowed myself future purchases. I don't think I've actually repurchased anything I've gotten rid of, but knowing I could if I decided to take up that hobby again, or found I needed another shirt, or whatever, really helps me let go.
This is a good way to think of things.
Crunchy Mama to my girly girl (11/07)
and my little dude (12/09)