There are no restrictions on any non-liquid main dish that is wrapped or in a container. Beverages brought on board must be purchased after clearing security.
All food must pass through an x-ray machine. For this reason, it is important for all food to be wrapped or placed in a container, so it does not make a mess. All natural foods, such as fruit, do not need to be wrapped unless they are partially eaten. Sandwiches, baked goods, and candy are all good choices with no restrictions to worry about.
Any liquid must be 3 ounces or less, which also applies to many popular food items such as apple sauce, puddings and yogurt. There is also common courtesy to take into account. For instance, foods that emit strong odors should be avoided as not to disturb other passengers. Possible food allergies should also be thought of, as some passengers may have strong reactions to items such as nuts. If flying internationally, you may not be allowed to bring your food with you when you leave due to restrictions enforced by the country visited. Passengers in need of medically required liquids, such as baby formula and food, breast milk and medications, are allowed amounts in excess of 3.4 ounces.