I collect books. When I like an author I buy all the books from that author one by one until my collection is complete. I also collect Harry Potter stuff. Though I haven't added anything to my collection recently, I used to by many HP stuff. I also have a collection of stamps which must be worth a huge amount already considering that there are less and less people sending stuff through snail mail. My husband collects Star Wars stuff and my youngest son collects Lego. What do you collect?