I try and bring one thing for each hour, and my dd gets a new thing on the turn of the hour. She is quite good at checking my watch to see how long she has to wait (we have a very long flight ,so I have to ration the treats like this, or they would all be gone within the first hour).
Playdoh was popular, so were pipe-cleaners, and sticker books, but the thing that keeps her the most occupied by far, is a walkman with headphones and story tapes - we got some great Playhouse Disney tapes (she was a bit younger than your kids, 4 1/2) and she sat and listened to Playhouse Disney over and over, she also liked some proper stories, ie just a voice reading short stories. I would say with a bag of tapes to choose from, she would have been happy without the rest of the stuff.
bev