C.R.
If you do not buy a seat for him he will have to sit on your lap the whole time if the flight is full. If it is not full they are pretty good about letting you use one for a little while. I have always taken my car seats with us on a flight. The kids are familiar with their seats and I think they fly better having their car seat. You will definately want to bring a sippy cup, but do not fill until you get through security. Is what we did when we flew my 6yr. old and 15 month old was we packed a little carry on for them. It included colors and coloring books, color wonder markers, and a couple of snacks.