Just something I started age 15 or so, basically snorkeling in 1969. I label my collection entries according to location where they're found, and in a logical order up and down coasts--from Arctic to tropical waters, almost all in N.A. It was the only reason I took OW course when we moved to the East Coast in 2005. Later I got interested in other aspects, like DMing. Nevertheless, the vast majority of my collection are shells found empty, many while beachcombing.
I do find it interesting that a majority of divers have little or no interest in shells and find them very boring compared to other aquatic life. I am the opposite.