Shells and Twine Bookmark: Craft a lovely bookmark to remind you of days at the beach. Natural string fits right in with seashore finds, such as shells, buttons, and bottle caps. Knot eight 18-inch-long strands together at one end to make the main bookmark; knot 8 inches below the first knot, or farther depending on the size of the book. Drill holes in items to attach to the string ends or use hot glue.