There are two coins I own, which I can't find. And, it drives me bonkers.
One is a 1932 D Washington quarter in very good shape. It is, by far, the most valuable coin I have ever found in circulation.
The other coin was given to me by our children, quite a few years ago -- a 1/4 ounce Gold Eagle.
While it's a little off topic, I also highly value an autographed picture of Harry S. Truman, personally enscribed to me. I'd like to have it on my office wall, but can't find it.
I hope I can find all three items eventually.