Andrea does he eat weetabix or any type of cereal with milk?
What I did for my 3hr flight to Spain, we write down his typlical routine (you should do this for 2 days) and note down what he normally eats - I took enough for each meal + enough oz of milk in ready meade cartons to cover the flights.
If you think there will be a problem feeding him certain types of food on the plane then you can try finger food - will he let you feed him finger food? (In your other post you say he still drops it) but if he lets you feed him, then sandwiches, breadsticks, blocks of cheese, veggies and fruit, etc may be a good idea. The cabin crew can heat up food, but it takes ages because thy can only do it on a jug of hot water, so if you intend to get them to heat stuff up for you, ask for it well in advance.
I gave Calum weetabix for his breakfast on the plane, I took the dry weetabix in a container then filled it with the relevant amount of milk - followed by chopped fruit, which DH and I fed to him. Are you able to take ready made cartons of milk rather than have the hassle of having to make up formula?
Do you always give him jarred food or are you only doing it for the plane journey?
Lauren x