Stereo Slides... I collect old stereo slides. I have thousands..some in obvious sets..some just misc... some as salesman sets.
I also collect old negs and prints when I come across them - have some cool glass plates as well as circuit prints and negs
recently found a whole box of exposed but undeveloped 120 tri-x rolls at an estate sale
gotta develop those one of these days
also..I bought an old kodak folder once that had an exposed roll in it..I developed it and it showed some army guy on leave circa WW2
that was kinda cool