what does your ds like doing? for on the flight, we take:
sticker books/magnet books
favourite books (Gruffalo etc) - dd1 loves books, so for her, it is heaven to sit and read/be read to for hours on end (not so for us, but we take it in shifts )
last year, for flight to Oz, i invested in an iPod Touch. Absolutely heaven-sent piece of geekery. downloaded toddler games (matching pairs, simple number games, etc), put her favourite dvds on (mr tumble and similar - we also have a portable dvd player for this, again can plug in my ipod, so have hours of dvd downloaded on my ipod - saves fiddling about changing/dropping dvds)
simple games like orchard toys ones (dd1 is 5, dd2 is coming up 3) so we all played a couple of rounds of shooping list, or picture lotto etc.
the ipod was invaluable for managing queues at check in etc, as easy to carry and whip out at crucuial moments. I would also recommend trunki suitcases - gives tyou an inbuilt toy to wheel them up and down on while wating in the queue. dh is tasked to talk to the check in person, sort out seating etc, while my job is to entertain children while we wait. i tend to ignore all stares, and sit down (out of the way) next to the check in desk, and read a story. unconventional, but it works (for a while). I developed a good line in stories about "two little girls" last year - coincidentally called the same as my dds, and talked the girls through what was going to happen. so eg, one day, the two little girls woke up and it was time to go on holiday. they drove to the airport, and when they got there, they had to talkk to the lady and get their tickets for the seroplane. it was abit broing waiting while their daddy talked to the lady, but they were very good little girls, and waited nicely with mummy and listened to a story" and then would sit down and get a book out... when it works, it works well. when it doesn't, it's a disaster, because you look liek a lentil-weaver ineffectual parent.... but my girls loved it, and especially loved seeing the similarity in what the story girls were doing, and what they were doing.
ime, it worked better to be telling htem as it happened, rahrter than in advance (although we do a lot of advance prep too) - it's sort of like an ongoing reminder of all the preparation for them, I think.
we still use the two little girls stories each night before bed, to go over what has happened in the day, and also prepare for the next day if necessary.
now that dd2 has her own seat and ticket oo, we can now pack 4x cabin bags, which we use to full potential.
dd1's is full of food/snacks for the journey
dd2's is full of toys/books/games (both trunki suitcases)
dh & I both take a wheeled cabin bag too - the largest wheeled small suitcase we can fit. we have: dvd player/ipod plus cables. change of clothes for everyone. nappies/wipes. and the essential comforters for each child (especially ipportant if the flight is a long one where dc are expected to sleep, ime. no way will dd1 sleep wihtout "sleepy bear".
I htink the key is to prepare for constantly entertaining in some way, then any minute where you don't have to is a bonus