M.C.
I just flew with my daughter a couple months ago when she was 16 months old. Like most everyone has suggested I packed lots of snacks. I had raisins, fruit snacks, teddy grahams, you name it I probably had it! I also bought a couple new books for her and new small toys hoping they'd keep her interested for a while since she'd never seen them before. I had a portable DVD player - I tried headphones...she didn't like that at all. She did watch it for a little while but then she was more interested in the buttons. I also brought paper and crayons...that worked for a long time.
I would suggest sitting towards the back of the plane where the drink carts are stowed. We sat back there and while the flight attendants were up I could jump up and let Ella play in the little cubby area or try to bounce her to sleep.
Best of luck to you!
Michelle