T.S.
Give yourself plenty of time to check in and get through security. Until you board, walk around a lot to get the little one tired. I always make a big deal of picking out something to drink (usually water and apple juice for us - I mix it together in a sippy/straw cup) or look at the planes out the window. Go to the dollar store for crayons, coloring/sticker books, thin reading books - do not give/show them until it the flight. Pack snacks and other food for you and her. We bring a portable DVD player as a last resort, too.
We always start with going through the inflight magazine, the shopping catalog, and then make sure she drinks through the sippy/straw cup to help her ears. Once we can put the tray down, if she's hungry start with snacks or food. Otherwise, pull out a coloring/sticker book. We also like the slates that you can write on and then move a lever and it erases. I use it to draw pictures that we can talk about or show my daughter letters and other things. If she sleeps, great - if not, pull out the DVD player after you've exhausted everything else.