I also travel a lot due for work and have tried many things, from having meal replacement packs and do them in the airport to making tuna sandwiches before hand.
However for convenience last trip (which was almost 8 hrs of travel time) I made a complete meal before going to the airport (by this I mean chicken breast, meat, tuna, rice, potatoes, etc.)... then I took some protein drinks with at least 40g of protein, like those sold in supplements stores, together with a meal replacement bar or carb bars (calculate according to your dialy requirements) If you can, or have connection flight buy a chefs salad or make a complete meal.
The food of the plane sucks and contains lots of sodium... also get a big bottle of water so that you can be hydrating because from changes in altitude you can dehydrate.
Take glutamine beforehand and after the trip.
Usually our meals are between 2-3 hours so you can plan your meals accordingly.
I know sometimes it sucks to rely only on protein bars... but I prefer it to have my food removed at duty and rely on airport food.
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