If you are going on a long flight, it is a good idea to take something healthy to eat with you. Some fruit or nuts are always great. Aircraft food can be pretty bad, unless you are travelling business class of course. It can also save you a lot of money if you bring some food for your layover.
You can spend a lot of money on a 7 hour layover in Doha by bringing your own food. So if you can bring some sandwiches and fruit with you, it can help a lot.