Whatever you do get to keep him busy, try and keep it out of sight for a couple of weeks beforehand, same with his trusty faves that you plan on taking, so they are like new again once you're on the plane.

I took a bag loaded with things, and honestly, the dvd player was the winner for us most of the time, along with pop corn.

Under 2's normally fly free unless you buy a seat, so he will be on your lap. When you check in I highly recommend asking if there are any spare seats, and if there are, if they are able to block out a seat for your DS next to/in between you two. We had excellent luck over Christmas and managed to get a blocked seat on all 4 of our flights, and it was a godsend!