During a long-haul flight, your body is coping with changing time zones, less oxygen to the brain, cruising speeds of 500+ mph (800+ kph), et. al.
The best way to offset these abnormal conditions is to eat and sleep during your flight.
In doing so, you will gift yourself with greater energy and decreased jet lag when you land.
Many long haul flights take place overnight—either night into day or day into night.
Whether you board your flight at 11am or 11pm, they will feed you a semi-substantive meal within the first hour after takeoff.
They do this for a reason… to knock you out (in a good way)!
It tends to go down like this: take off… drink service… food service… l-o-n-g cue for the bathrooms… the cabin lights are turned down real low… the cabin gets nice and quiet… most of the passengers end up nodding off soon thereafter.
If you’re not too keen on eating the meals catered by the airline, bring at least 2 fulfilling meals of your own.
Additionally, be sure to pack a snack or two in case you get a lil’ hungry between meal services.
Note: Normally, there are two meal services during a long-haul flight, plus a little snack handed out at the midpoint. For most major airlines, this is included in the cost of your airfare.