C.B.
The most important thing is to make sure he is drinking on take off & landing. I always planned it so my baby would be thirsty/hungry at take off & landing. Don't give him it to early or he'll drink it all before assending. Wait until just after leaving the ground.
I also took little snack bags with different healthy bitesize snacks. That way when he gets fussy you can pull out something 'new'. The same with small toys. My granddaughter is now 14 mos & loves to color so bring lots a paper & a small box of crayons.
You also can give him medicine that makes him tired. Only you know which ones do that. Benedryl works for some & works opposite for others. When my son was two our pedi gave us a rx of the stuff they give kids for surgery. Well it worked opposite & he was a raving maniac. It was awful. So try the medicine out before the trip to make sure it works and only use it if all else fails. I wish you the best of luck.
Aufeidersein !