I think for most of involved in this hobby, we've always been collectors. Over the years, I've always saved stuff, even if they weren't proper collections. As a kid, I saved all the cardboard backings on my action figures. And Lego directions. And the boxes to my old video games (which I threw out about 6 or 7 years ago, right before realizing that some mint video game boxes sold for almost as much as I had paid for the games new). I collected sports cards and Pez dispensers, and stamps, and whatever else seemed interesting to a kid.
And among all that "stuff," I saved ticket stubs. As a kid, we went to a handful of games a year, so my stub collection was more a couple scraps of paper in the back of a binder. As I got hit my college years and PNC Park was just a short walk away, that number grew tenfold. And so did my stub collection.