So you'd want things which don't desperately need chilling ideally? What about fruit, savoury muffins, dried fruit, vegetable sticks, water for drinks, cheese scones, slices of no added sugar cake. That would be a fairly balanced meal even though it's all snacky just in case the aeroplane food is awful. Lots of planes do sandwiches though but I have to admit I'd do the same. Even if he ate the aeroplane food, when it is hot it tends to be nuclear (and awful) and when it's sandwiches you might not have a choice on filling.