I had good luck at rummage days and a nearby neighborhood-wide yard sale.
A shoebox of stamps. He wanted $15 and we settled on $10, and as soon as I walked away I was kicking myself for not really looking at the variety of stamps because I could tell there were a lot of American flag stamps which I really, really don't need. However when I got home and went through them there really weren't that many, and I was still left with a good amount of stamps I could use.
I love office supplies, especially those that come in tins. Here's a tin of "12 drawing pencils" - that still has two pencils left inside. Certainly worth the 50 cents.
Little half-full boxes of tiny staples from a garage sale, which will help to use my already established tiny collection of tiny staplers.
