R.S.
My 23 month old daughter goes on planes frequently with us. What has worked best for her ears when landing is for her to chew on ice chips. She loves to play with it, it is healthier than candy, and the swallowing/chewing of the ice seems to really help her ears. The stewardesses will happily give you ice a little before landing if you ask (you have to ask earlier enough b/c they do close the kitchen before they land). As for entertaining her, we read lots of books, we point out things out the window (trucks, planes, before we take off, clouds, mountains, etc after take-off), we try to give her a new toy or two as well as bring some of her favorite ones, and we take many walks to the bathroom. She loves walking up and down the aisles and usually people don't mind. We now buy a seat for her but before we did (and when she was smaller) we'd bring the ergo and stand near the restrooms and rock her in it when it came time for her to go to sleep. Also, as others have suggested, we try not to have her nap as much as usual before the flight so she is tired when she gets on.