Well I prepared for the worst flight ever and was very nicely suprised! DS was so good... It was well worth paying for the extra seat on the way out when we could have a pile of toys next to us, and weren't squashed next to a stranger. DS enjoyed stickers, bubbles, books, a squishy light up toy that I'd got new for him, and he played with a cup of water for over half an hour (trying to drink it with a fork, and dipping empty food cartons in it)... he scrambled back and forth across me and DH a fair amount, but we only went walk about around the plane 2x... He wouldn't wear the headphones we had purchased... but we spent a while playing with new books. Lift the flap ones were great.
I also found that the background noise on the plane meant that a few simple musical toys (his phone and a lift the flap book with noises) were not disturbing to those around us.
One other thought for people... the 3 year old behind me kicked my seat and whined a fair bit - but I have to say this was preferable to the way her mother was getting more worked up and cross with her. I prefered the child being fed up to the mother shouting at her and telling her to shut up and stop being so stupid etc etc...