These ideas aren't original, but they may help.
Wrap new items and let them unwrap one every so often.
Have a bag with interesting feeling things and let them reach in and choose something without looking (I had a fuzzy lamb, plastic bracelets, pipe cleaners, squishy animals etc.)
Bring magna doodle type drawing tools.
Chalk can be used on the pull down trays and then wiped off.
Tangle jr. is fun and all one piece.
Portable DVD player(s) are cheap and helpful. Take your children with to buy headsets, to make sure they fit them comfortably and will stay in place well. We found that the ones with larger ear pieces(that cover the whole ear) tend to work better and adjust smaller.
Bring their carseats (I found that the kids stayed in them WAY better than just on the airline seats, because they were used to being restrained in them in the car.)
If your children tend to throw things, think about tethering them (I used self-stick velcro and then had one tether with the matching velcro on the end of it).
Get kid leashes for in the airport and then let them go on their own power as much as possible (to use up the energy they can't on the plane). I got the best laughs out of my three-year-old when people saw her just running circles around me.
Of course bring their favorite snacks, even bring a few new ones, SMARTIES necklaces are candy, but they are not sticky and they take a while to eat AND it helps develop important muscles for talking. Pull and peel Twizzlers can also be pulled apart and eaten by putting one end in mouth and bringing the rest up without using hands.
In other words don't think about the most efficient way to do anything, think about what would take the longest and still be fun.
Gate check your stroller, and use it to transport the car seats in the airports.
Freeze water in sippy cups (about half way full) and use when they come around with drinks (getting up is impossible with a tray down and you can put the sippy cup back in the bag or on the floor without worry) I even used a cup with lid.
Also, if you think your kids will have a hard time taking a nap at the appropriate time or sleeping for the night, some doctors recommend Benadryl (but try it first to make sure it doesn't do the opposite). I have also had success with Melatonin, it is used by business travelers to combat jet lag and get on the new schedule. It comes in a liquid form or chewable (my kids were helped by an amount as small as 1/6 of 1 mg) it just helps them get sleepy in a calm darkened environment. For the chewable/liquid, check your health food store (GNC WHOLE FOODS, etc.)
About me: I have traveled every year with my kids, starting when my oldest was two and the next was 4 weeks (and it was just the three of us). I now have four children from 10 down to 14 months. I wish you the best.
K.