I collect bottle caps, geological specimens, and "Lithicoins" which are coin shaped mineral samples. There are other things I collect that also have a purpose beyond just looking interesting/nice such as: books, board-games, computer games, training weapons, single board computers, and so on, some might say these don't count but in my mind they do. edit: I've also been looking into starting leaf/flower pressing with my kids and starting a collection for them.