Unopened in My Collection: 1989 Topps DoubleHeaders
Maybe I had bad taste -- I really liked these 1989 Topps DoubleHeaders, back in the day. Each one is a plastic stand which contains a player's "rookie & 1989 card -- back to back." But they're not really cards at all. Inside the plastic stand is a thin sheet of paper which has an image of the front of the rookie card on one side, and the front of the 1989 card on the other side.
A full box of 24 unopened DoubleHeaders, plus two more.
The backs of the two loose DoubleHeaders, showing checklists.
I have a full box of these unopened (containing 24), and two more, for a total of 26. I know I had a bunch of them that I did open, and which I displayed on my bookcase. Either I (or maybe my mom!) must have thrown them out at some point. Like I said, they're not really baseball cards, so I am fine with having lost the ones I opened.