Honestly the thought of sensory issues, lack of sleep, the time change and strange food would scare the bejeezus out of me. My first reaction is Benedryl. My doctor prescribes it as a sleep aid and it works for my Bear (it can wire some kids though so test first). Having him get some sleep will make the rest of the flight more bearable for everyone.
Also lots of times the pilot will give a tour of the cockpit to kids, but that was awhile ago and they might have changed the policies with the terrorist issues. Doesn't hurt to ask.
My other cure for long trips, the window seat! Also try to let him walk up and down the aisles some.
