You know, some people collect stamps, others different kind of coins, etc.
So what do you collect? And how big is your collection? How long have you been collecting?
I myself collect commemorative €2 coins. Even tough my collection only has 4 coins in it (2 of which being very common), it's fun to look at your change and see you got another special coin. I didn't start collecting them untill 2-3 months ago by the way.