Pack devices, chargers and back up batteries. Whenever possible charge so that all devices are as full as possible for as long as possible
Comfy headphones for all, if you have ones that need to be charged, see point above and take a back ip pair of normal ones
Layers of clothing and a hoodie on the top, the hood can be used to cut down the lighting if they want to sleep
Each child has to carry their own bags thru the airport
Each child needs a neck pillow, pick one that can be attached to the outside of their carryon bag
Each child should pack a bag of snacks they would like to eat. Make sure they also have a way of clipping shut anything that is larger than a single serving, some wipes and a rubbish baggie. One of my dc always packs a huge tube of crackers he likes and a clip, the other packs individual raisin boxes and pretzel packs, the third prefers meat jerky and crisps and the fourth always wants to eat the plane food and sweets - so I make him take some back up carby things
Pack a long lasting sucky style sweet or gum for each take off and landing to manage ear issues. Remind them to not put it in their mouths until the last minute
A collapsible water bottle for each person, fill it once you are through security (there are always water fountains. Open with caution once you are in the air as the pressure will change
Remind them about bathroom etiquette on the plane, and they cant just go whenever they want (seatbelt signs on, takeoff and landing) floors will be awful, dont let trousers legs drop onto them and always wear shoes etc
Remind them that their seat back is someone else’s tray table and their tray table is someone elses seat back and so they need to be thoughtful .
Talk through the entire trip before you go, so they have it in their minds eye and can plan their own patience accordingly.
Consider letting them take the lead in navigating through the airport, checking in, finding the gate so that when they need to do it themselves solo, they have an idea as they havent just been trailing mindlessly behind you for years and not engaging their own brains
See if you can start to time shift your body clocks before you go to minimise jet lag..so get up early/late. Shift meal times by a hour and then another hour (if possible)
Have Fun