That turtle shell would make a very nice pouch once you get the moss and barnacles off of it (and get the turtle to vacate his premises). The one or two I've made were pretty basic once you just have the shell to work with. The shell, a piece of leather, and the strap material are all you really need. Cut the leather to shape and size to cover the perimeter of the shell, plus some overlap for the flap on the top, punch or drill corresponding holes , and lace the leather and the shell together. However many lacings you think you need, you'll actually want about twice as many.I don't remember how I put the strap on, and the last one I made is two states away. You may want some doo-dad on the end of the flap, just to give it a bit of weight to help keep it closed. Be real careful so you don't leave sharp pieces of bone on the inside of the shell which would cut you when you hastily put a hand in or out of the pouch. You do NOT want an infection from a turtle shell.
I used to take a slaughtered turtle or two to Friendship to give to the guys and gals at the pistol line, in appreciation for making me feel welcome at Friendship. Nobody ever said "No thanks" to free turtle meat!
Oh yeah, the feet make great back scratchers when mounted on a stick or dowel rod. I've yet to figure out anything crafty to do with the plastron.