You could also easily have 5 store credit cards (J. Crew, Banana Republic, etc.) for extra discounts, a few gift cards you haven't spent yet (Starbucks, Best Buy, etc.), an extra 3 credit cards (they have different promotions), a handful of loyalty cards for discounts (a couple supermarkets, three or four coffee shops, a couple of restaurants), various forms of ID and access cards (company, school, gym, apartment complex front door)...

You can see how it adds up. The reasons for almost all of them are discounts or extra value. Keeping track of all these cards and carrying them around could easily save you several hundred dollars a year if you're willing to do it.