Food:
American Box turtles are omnivores and will eat fruits, fungi, veggies, greens, mollusks, worms and insects. Wild turtles, we know they eat plants for almost half their diet and animal foods for a little bit over half their diet. They eat what they find. Another word are opportunistic feeders, willing to eat almost anything edible that they find. So focus on using a wide variety of foods. Feed the turtle on a flat rock rather than from dishes of any kind. This more natural approach will prevent the beak and toenails from becoming overgrown. Provide a high calcium source all the time--e.g. cuttlebone, boiled eggshells, plaster block--so that the turtle can munch when it feels the need for more calcium.
It even produced Scat!