T.H.
I just got back from a trip with my 2 year old and 5 month old and it was easier than expected. She (2 yr old) had flown multiple times before but now that she's older and even busier I was worried! It was cinch, really! First of all, I would recommend taking the car seat onto the plane. Your son is used to sitting in that seat and will probably fall asleep in it easier than the regular plane seat. Also, pack some snacks, of course, but I wouldn't recommend drugging him. Don't overpack b/c you'll just regret lugging all that stuff around. If you have a DVD player, I would only add a couple books and maybe some crayons or a different toy. I bought the I Spy Snap card game to look at the different pictures on the cards, not to play the game. By the time you board, listen the safety speech, take off, etc. there is so much to look at and talk about that you'll be an hour into it before you know it! As far as bringing liquids, you can do it in small quantities and only for the child, not for you. Just declare it when you get in line and it shouldn't be a problem. I also carried on the Tylenol, hand sanitizer, etc. and it was fine, just put it in a quart size bag. Our daughter doesn't use sippy cups any more and I noticed that they now have lids and straws on the airplane for the kids, which was so nice and unexpected, so you may think about going that route too. My last suggestion is to take some balloons for the waiting area. They are cheap and easy to blow up and you can leave them there or throw them out when you board the plane. Your son will have a great time and it's a great distraction from waiting for him and other kids there!
Have fun!