If other places are full, Fosshótel Húsavík has both a standard-issue restaurant and the more atmospheric Moby Dick Pub (tel. 464-1003), which serves burgers, pizzas, and pastas. Bákari (Garðarsbraut, off Mararbraut; tel. 464-2901; June-Aug Mon-Fri 8am-6pm, Sat 10am-4pm; Sept-May Mon-Fri 8am-6pm, Sat 10am-2pm), indeed a bakery, has sandwiches as well as baked goods and could pass for lunch.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.