I would say on the plane is the easiest to keep them occupied. I usually bring my dd toy laptop, my ipad, books, and snacks. These items keep her busy on the plane.
At the airport, totally different story. She's either in her stroller screaming her head off and trying to flip her body out of the stroller. Or finally I give up and let her run around the airport which results in bad looks and her tiring mommy out fr an hour. This is when I wish I could get her occupied with something else.