I collect empty space. 😀
I don't collect anything per se, but if I see something industrial, strange, odd, old, connected with art or print work, preferably Art Deco or Googie, etc, I buy it.
I have an antique Underwood typewriter in almost pristine condition, old printing blocks from newspapers, numerals from old gas station signs, an old Art Deco desk fan, and a weird old machine-shop tool my grandfather made from scratch like 70 years ago. Completely unrelated stuff, but somehow all related.. you know?
I used to collect stamps. No offense to philatelists, but that was BORing. 😛