I fly back and forth to South America with my 2 kids and started doing it when my daughter was 3. Okay, here are some tips:
1. Get a window seat for your son -- it is both easier for him to fall asleep there and looking out the window while they load the plane, at take off and until you are up in the air will fill about 30 minutes of the trip.
2. Pack his own little carryon, even if it is a backpack, but don't bring too many toys -- just maybe the one that is his favorite to sleep with, a book he likes, and some paper, a coloring book, and crayons or colored pencils -- the coloring will be another 1/2 hour to an hour of entertainment on the plane. If he has another toy that will keep him occupied for another 1/2 hour or so, bring that. But, the worst thing is to bring something with little pieces that fall on the plane floor and frustrate him. One thing I do is get my kids something special for the plane ride and reserve it until then, so they have a new toy to play with -- it doesn't have to be expensive, just practical -- it can even be a new coloring or puzzle book.
3. They won't let you bring drinks or snacks on the plane with him, so don't. I had a TSA agent literally take a cookie out of my four-year old daughter's mouth and throw it away, which didn't end well, as you can imagine. Part of the fun of the plane ride is when the stewardess comes around offering drinks -- that's another 15 minutes gone out of your plane ride.
4. At that young, you might want to take a small umbrella stroller with you to the airport -- the really cheap compact kind. Usually the toughest part of traveling with kids is not the plane, but checking luggage, going through security, walking to the gate. Being able to strap him in the stroller and zip through the airport will make yours and his life easier. They will gate-check your stroller and have it waiting for you when you debark the plane.
5. All car rentals will also rent you car seats for fairly minimal fees. I would not bring my own car seat -- 1.) because they are a major pain to lug through an airport 2.) because they aren't necessarily that stable on the airline seat 3.) because at 2, for an air flight, he doesn't need anything more than the lap belt to keep him from bouncing too much from turbulence and he will be much more comfortable with just the lap belt -- more able to play and reach the tray table, etc. -- therefore happier, which is good.
6. Most hotels will bring a crib or single cot to your room-- just ask them when you make the reservation. I would not take a pack n. play. It's more expensive but if you can get a good deal on a suite, it will make your life easier. That way, you can put him to bed in the bedroom and you and hubby can hang out and watch TV until you are ready to sleep.
7. This is out of order, but finally -- the best way to get him to sleep on the plane is tire him out. When I fly to South America, if I can, I spend a night in Miami. The next a.m., I take the kids to the beach for 2 to 4 hours and get on a plane in the afternoon. They crash. I know that when you are packing to leave, everything is hectic, but if you can send your hubby to the park with your son for about 2 hours in the a.m. and let him run off all that excess energy, he might be more fussy in the airport, but fall asleep as soon as the plane is in the air. If instead, he is watching videos in the a.m. while you are doing all your last-minute stuff, he is going to be just full of energy because of the excitement of traveling.
I have a very hyper son. From experience, you will be surprised at how well he behaves and if he fusses and bothers people, don't worry about it. That's life.