I have collected something or other - besides dust, that is - nearly all of my adult life, and I have found that people who collect one thing often collect more than one, and sometimes many different things. My most serious collecting interest has been antique American pocket watches. I've published a book and a dozen or so research articles on antique watches over nearly thirty years. But I also have a modest mineral collection of about seventy specimens, and a six-item fossil collection. At various times I have also put together very small collections of US Coins, ancient Judean coins, fountain pens, and even old, out-of-print books on sea music.
I'm interested in hearing what kinds of collectables excite other folks.