Cookbooks, especially vintage ones. I love old hand written recipes. Once I bought a recipe book at a garage sale, and noticed a recipe where the writing was familiar. Turned out that it was from the grandmother of one of my colleagues. She passed away and her son gave it all to Goodwill. The book ended up in the garage sale where I bought it. Then I returned the book to my friend. Her mom was so happy to see the book again. She eventually gave it to me, it really is a treasure.