Good idea, we never fly without our portable DVD player. It's a special treat for him on the flight and he loves it. You can turn the volume down, and over the drone of the plane's engine, you won't be disturbing anyone either.
We used an Insignia at first, which worked well, but since you need to use the battery on the plane because you can't plug in - the battery is bulky on this model and if it isn't connected exactly right, it actually won't charge. Then you are stuck with a dead dvd player on your trip. So we switched to the Coby - works perfectly, is inexpensive, and the battery is built in. So it's smaller overall and you don't have to worry about whether it's connected properly when it's charging. The charge holds for at least 2 hours.
Also I have to throw this in here since it's your 1st flight with him - try to get your little one to drink something during the ascent and descent of the plane so that his ears don't build up too much pressure. If he doesn't want to to drink anything, massage his ears during those parts of the flight.
Have a fun trip!!