Food-borne illness isn't a threat only at picnics. It can even occur with your brown-bag lunch. To avoid problems, make sure you wash your hands before and after eating lunch at your desk, according to the American Dietetic Association. Other tips: Refrigerate your lunch when you arrive at the office. Thaw frozen foods in the refrigerator or microwave, not on the countertop. If you bring leftovers for lunch, reheat them to a temperature of 165 degrees.