Postage stamp collecting or philately is the most popular hobby in the world.

I used to be a great collector of things, anything at first, bottle caps, shells, frogs, pets, dead animals (mostly birds). It got a little strange there for a while, hair, weird clippings from the paper, receipts, dead birds. Mostly junk. Broken furniture, old TVs. I always think I'm gonna do something cool with them, like a great art thing, funky, cool. I have a hard time passing up thrift stores. I thought maybe i was going crazy for a while. Like I was compulsively shopping for stuff I didn't need. Maybe I was gonna turn into a pack rat? My mom was one, it could be passed on to me right? I have tried to convince my self that just because you are compulsive and need to pick something useless up and bring it home that you're OK. Those who view collecting as trivial or a waste of time, miss the connections that it has to life skills and occupations. Scientists also collect things; they gather information, data, and samples. Museums and libraries are collections. Many people make their livelihoods by collecting and disposing items. In fact, all of us go through our lives collecting and discarding things around us.
Maybe I'm not insane, maybe it's a hobby or maybe I'll end up like the most famous compulsive hoarder of all, Langley Collyer, who for 15 years filled a New York City mansion with 120 tons of trash, including 11 pianos and all the parts of a Model T Ford. He and his reclusive brother were both found dead among the clutter, having died just days apart. Langley had been crushed by falling debris.