People love to collect stuff. I'm sure we all do. Some of us just do not know it because the interest is lying in our subconscious mind, but they are still collecting nevertheless. Don't you realize that you have probably been collecting garbage all these years?
Arguably the most famous item of collection is the mailing stamp. Why do people collect stamps, anyway? It's probably for commemorative reasons. Stamps represent a phase in a nation's history so enthusiasts might like a stamp for its historical value. It's also probably for economic reasons. After all, with stamp collecting being a widespread hobby, it's relatively easy to get profit out of it. And, of course, it's probably for personal reasons. "Remember when we were kids we used to stick stamps on each other's noses?" or something to that nostalgic effect.
Aside from stamps, virtually everything on this planet can be collected (or, if you are a wealthy fellow, you can even collect stuff located outside this planet), some of the most famous of which are trading cards (Oh, my friends used to collect these; they'd regularly exchange their collections just to brag when they get a certain rare card or something like that), pottery, jewelry, and I do not know what else.
Some would even go further to collect items such as guns (and buy vaults for them, too) and other slightly dangerous items. Some people put so much money into these collections that they cannot part with them whatever price they are offered. I like these kind of people. Money's purpose, after all, was to make its makers (humans) happy, so why would you exchange so much time and effort for something you can earn through other means, anyway? It's a different case, of course, if your sole purpose from the very beginning is to gain profit.
Whatever you collect and whatever reason you have for collecting them, good luck!