The Day of the Flight!
I have heard many parents try to keep their child up later at night or skip their nap the day of traveling in hope that the child will sleep longer on the flight. This is travel suicide. Step away from thought immediately. A rested child is always a better child on any flight. Keep excitement level high and stress level low. Kids pick up on all those vibes and will follow suit.
At the airport. The fun begins finally. Bring snacks - I have yet to see a child eat anything that is associated with airplane food. My daughter will try anything - its become our family's favorite pastime to watch her try unrecognizable foods...but airplane food she will not touch. I do not ask anymore. When my youngest finally had his own airplane seat (and inevitably his own tray of "food") I didn't even take the aluminum cover off the tiny meal plate - I just reached for the plastic covered cheese and rock-hard bun for him. I know now. SO I bring a combination of healthy, light (in weight) snack options. Pretzels, nuts, grapes, cheerios seems to work best for us.
Milk - Airplanes have milk so that’s something you can cross off your list. You need to bring formula or any specific milk (soy or almond) though.
Security - most times if they see you schlepping kids, they will pass you to the front of the line (I think the only advantage of traveling with young ones). The trick is for them to see you so if your kids have a tendency to be loud, this is the time to do it! At the gate? Run. Run. Run. Let them get their steam out. I strongly advise to let them run up and down the aisles, the waiting room, anywhere! if needed, chase them; help them get exercise and hopefully, exhausted!