1) Hogfather, by Terry Pratchett; copy for me and two copies to gift, plus the ebook, and the audiobook 2) Mathemagics, by Benjamin and Shermer; it teaches how to do math in your head. I've bought it for personal use three separate times, about 15 years apart.
Sophia_Nyx 🏳️⚧️Name physical media you purchased more than once.