Definatly give some motion sickness med or have one of the braceltes on before you go.
I agree with the rest - lots of activites and snacks. If I can keep giving my kids food, they'll hang in there much better! LOL
Cards, books, anything small that you can pack and a variety of activities is good.
We took our son on a plane when he was 9 months and was just getting over an ear infection. BIG MISTAKE! He was miserable, got sick again at our desitnation and was sick on the way home - I guess the altitude messed with the fluid in his ear and the infection flared up again.
Try to get a row where you can spread out a bit. We are 4 flying together now and ask for 2 rows and in each we get the isle and the window - leaving the mddle seat empty. It will only be filled if the plane is really full. THEN, the person there will GLADLY switch with one of you. Who wants to be between the mom and the kid???
But, if the plane is not full, you;ll have an extra seat.
Good luck!