Hi J.: I have never responded on mamasource, but this is a subject about which I actually know alot! I have traveled extensively with my son from the age of 2 months on -with and without my husband - across country, to various locations in the U.S. and abroad, so we've actually been on flights of 12 hours or more. He is 10 now and a wonderful world traveler, so I guess it pays off.
Yes, I always had a bottle ready for my son for take off and landing as it can help with their ears. I think you need to look at the TSA website (I believe it's www.tsa.gov) and see what the current rule is with respect to bottles for babies. I believe there is some special rule where you can bring a certain amount of bottles, liquid formula, etc. If not, you should see if you can get powdered milk, formula or whatever you feed him and bring that in your carryon. Once you go through the security checkpoint, you can buy water to mix it at any of the delis, etc. I also found that the flight attendants were very nice to us and would give us water, milk, etc. in flight. I would not, however, depend on that. They are sometimes very harried before take off and don't have time to get out galley supplies.
As for the car seat, if is is FAA approved (there is usually a sticker on the seat), you can bring it on the plane. If you do not have a ticket for your son, you can sometimes get an empty seat so he can sit in his own car seat on the plane. Flights these days are more and more full, but you can probably bring it to the gate and find out if there are extra seats. If not, they can gate check the seat for you. I would also mention if you are renting a car, you can ask for a car seat, but you may be more comfortable with your own.
When my son was as young as yours, I would basically bring some of his books and favorite toys to keep him busy. Just be prepared to be fully engaged reading to him, playing with him, etc. I also found that for several years, my son loved stickers. I carried a small notebook with me and several different kinds of stickers. He would basically pull them off the strips and put them in the notebook. As he got older, he would supplement the pages with stickers with his own drawings. He loved it - and we kept the notebook and he still gets a kick out of looking back on it.If you are lucky, he will nap on the plane, but otherwise, I think you just entertain him with what he is used to. Have fun!