Back up battery bank for devices and wall charge them whenever you can
test run headphones before you go with a no headphones no device hard rule
get a bag of child safe hard boiled sweeties on sticks or something they can suck on that will last at least 10 mins. Unwrap while you taxi and then give them to both dc as the plane accelerates for take off. It really helps their ears pop. Repeat for landing but you might need two as it takes longer. Dont give them too early or they finish them too soon
if you have any liquidy snack or sippy cups that are sealed, open them with extreme caution once in the air as they might explode everywhere from the pressure change
take some sealable plastic bags to use for rubbish/clothes covered in vomit/poo
take lots of wet wipes
if you can, dont let them think they can unbuckle their seat belts. If they think they have to stay buckled unless going to the loo, then you wont have to fight them over playing the watch me unbuckle and crawl around in the footwell game.
exhaust them physically before getting on the plane, find a quiet corner and play run and touch the window and then hop back to me
take a blanket to thrown over them, planes can be cold and it can be useful to block out the light
comfy, easy change clothes and shoes
dont expect to get any rest/sleep yourself. Pack yourself some emergency chocolate snacks!