We've been flying with our 23 month old since he was 8 weeks old, including two trans-Atlantic trips. Our strategy since he was about 14 months old is to try to schedule take off to be just after or during a usual naptime. If we can't then we try to alter his schedule to make him sleepy when we take off. We ALWAYS pre-board so that we have a drink (sippy cup) and snack ready for take-off, as well as some toys. Let him stand by the seat or on a seat while everyone else boards. Robbie says hello to everyone as they board and waves to them. Then when we sit down, he stands on my legs and faces the back of the plane so that he can see everyone. He thinks he is on stage and behaves very well. When it is time to actually take off, he has to sit in my lap but that is when we break out the sippy and special snack. IF we are lucky, by the time it is okay to get up again, he is asleep.
We always bring his favorite blankie and his favorite doll, Elmo! We also have had him fly in footed pajamas up until now so that he is plenty warm and comfortable. We leave next week to go on our last trip before he turns two.
Other things to try, finger puppets and games, like 10 Little Monkeys, WHeels on the Bus, Itsy Bitsy Spider, WHere is THumpkin, etc. Think positive too, because they pick up on it if you are nervous. Just tell him that the captain said he has to sit, show him the seatbelt sign, etc. As long as you are trying, the flight attendants are super nice.
Good luck!!!