Morning traffic in Duck includes the sidewalks, filled with walkers, joggers, runners, and bicyclers—many of whom will be carrying bags, boxes, or buckets of Duck Donuts. Each doughnut starts with a coating—traditional favorites like vanilla and chocolate, or more daring varieties like lemon, peanut butter, and maple. Then, you pile on toppings like shredded coconut, chopped peanuts, sprinkles,...