UPDATE: Please review current airline policies for meal service. Due to ongoing COVID-19 restrictions, some airlines have existing meal service modification in place that may affect typical meal service.
If you are wondering about meal service, pick up the phone and call the airline you are flying to inquire.
There are certain flights that will never have meal service. You can find this out just by looking at the length of your flight, and the time of day you will be flying. Flights less than 2 hours will only have a snack/beverage service. Some airlines have meals on short domestic flights, but you could be charged for it. Each airline has its own set of policies concerning meals and snacks.
On international flights that take you through a traditional mealtime, you can expect that a meal will be served.
If you have a special dietary need (diabetic, veggie, etc.), ask the airline if they offer a special meal.
You can bring along your own snacks as well, but check to make sure what you can or cannot bring.