Not all airlines serve a delicious meal, and so a good idea would be to grab something to eat before you board. Airports have a large number of local and international chain restaurants everywhere and it won't be difficult to find something you like. A cup of coffee is also a good idea before your plane takes off, especially if you need caffeine to keep a clear, focused head.
On the other hand, a few exclusive airlines do serve a great meal, something that you definitely shouldn't miss. If you are flying one such airline popular for its meals, a light snack or beverage before the flight is a better idea instead of a full lunch or dinner.