Get on the plane last, if you can. Otherwise you'll be sitting around with people packing the overhead lockers for at least 45min before the plane starts moving. Some airlines will let you take the buggy right up to the door and bring it to you at the door of the plane when you land.
Get a bulkhead seat with a bassinet - more leg room, more playing room and the bassinet is useful for storing things even if he is too big to lie in it.
Don't give him the bottle/boob until the plane is actually speeding down the runway. If you start earlier you may find that he's finished before take-off! Little chewing foods are also good, such as grapes or little chunks of flapjack-type bars.
Well before the meal is served, or immediately after it has been cleared away, take him to one of the doors (often at the back of the plane) where there is a bit more space without any passengers' legs, and do a bit of jumping around with him to work off some steam.
Pack a bag with whatever books/toys/extra foods you bring, but only take one thing out at a time and return the previous item to the bag. A mixture of old favourites and new toys is good. My dd loves catalogues such as GLTC, Little Green Earthlets, Blooming Marvelous, etc, and they are lightweight, pakc thin, can be ripped up and left on the plane - ideal!
Pack two meals for him in your carry-on bag - convenience and low sugar are more important than nutrition - in case of delays or spillage. Ditto at least one day's worth of nappies and wipes, and a change of clothing.
I was very apprehensive, but it was fine!