Use sea shells to key rings/ book marks
How can I use sea shells to make key rings or bookmarks
You can drill a little hole in a strong shell to attach to a key ring. Maybe glue small shells to the top of your homemade bookmark.
Here is how to drill a hole in a shell to make crafts: https://www.craftylittlegnome.com/drill-a-hole-in-a-seashell/
Good suggestions by Kelli and Adrienne. A couple of additional ideas: