When planning air travel, remember to request a special meal. Airports are harder, as are other terminals. Pack some food with you is the best advice. An apple, a nut butter sandwich on non-wheat bread and a small bag of almonds can tide you over without doing too much damage to a diet. Your own small bottle of water can help you avoid the liquid junk they sell for too much money in airports and terminals.
Restaurants increasingly offer a vegetarian dish.
At such restaurants, a baked potato and iceberg lettuce salad may be the best you can do. Several of the fast food chains, including Wendy's and Carl's Jr.'s, now offer salad bars, and again, with your own salad dressing, they reasonably good. You can get a bean tostada without cheese or just pintos without cheese for well under a dollar. In better restaurants, explain that you're on a strict diet and ask the waiter what the chef is able to prepare for you. You may end up with the steamed vegetable plate.