How far away is the trip? Have as many practice "flights" as possible. Meaning start by sitting in a chair or on the sofa for an hour increase it by an hour at a a time. You can use a the belt from a bath robe as a seat belt. You will sit next to him while the two of you pass the time reading, playing travel games, watching a movie or playing a game on hand held dvd player or a leap frog travel just like you would on the plane. Fit it all in a backpack, snacks included.
Then see how he does.
If you need more help you can ask your pediatrician for a sedative. I STRONGLY URGE you to try it out a day or two before. I have a niece who bounces off the walls when she has benadryl and it is supposed to knock her out. I take dramamine for motion sickness. If you have never had him on a boat before either, you may not know if he will get motion sick. You may want to be safe than sorry and talk to the doctor about the right dosage for that as well.
The time to find out what does or doesn't work is days before the flight.
As far as snacks so long as it is not wet it will be o.k. to take on the plane. NO jello, pudding, fruit cups, tuna salad, chicken salad, dressings or dips or gravys. I take trail mix and you HAVE to buy drinks on the other side of security. Some good options would be dried fruit or nuts and seeds. My favorites are dried cherries, cranberries, raisins, banana chips, sunflower seeds, pumpkin seeds, cashews, hazelnuts, pecans, and almonds. Peanuts can be dangerous for other passengers with allergies and so as a courtesy I will not bring them on a plane, especially with so many other options it is an unnecessary risk.
If I or my child had a lethal allergy I would want the same courtesy and respect extended to me.
Airplanes and airports really dry me out, so I always have a water bottle. I find it difficult to stay hydrated and sometimes get bloody noses. They do not serve meals or snacks on most flights any more even on long ones and if they do you will need cash to pay for them. They are still serving drinks, it's about half a can over ice. That's why I have a water bottle.
You may also need $1 to $5 dollars to buy "special" earphones to watch an in flight movie depending on the airline.
When you do get a break at the airport find a corner or area away from traffic to play relay games to use up some of that energy or if you can find a ball on a string you can even play catch.
As far as discipline, all you can do is take away his toys if he doesn't listen. You must keep him buckled no matter what and if he is throwing a tantrum stand up and apologize to the plane and let them know you are doing you best to calm him down and that you understand they want him quiet. You will have more support if they know you are trying and you empathize. Yes, there may be people who don't care and are not particularly nice about it but most of them will understand.
You are going to have a great trip,
L.