I have never permanently lost anything, however, after doing the back roll into the water I looked down to see a weight pouch laying in the sand about 20' deep. It was mine. :) When I went to pick it up I found a new lobster catch bag, also mine. LOL. Looked like a yardsale on the ocean floor!
On the other hand I have found all kinds of stuff. Watches, fishing poles, hoop nets and at Lake Powell I found a chrome box anchor at about 60'. Took awhile to get it up and I still use it on my deck boat here in Canyon Lake. It will hold 3 boats, no problem.