1) Continue to carry a spare pair of underwear for your 4 year old child. Of all days, they will need it on a travel day. Especially after a bad airport grilled cheese sandwich. You will know when "it's happening" because the child will get very serious but start walking like Yosemite Sam at the airport. R.I.P to his "Tuesday's".
2) If you buy any reading material for your personal enjoyment, immediatley dispose of it in the nearest trashcan as you will not read any of it.
3) As you enter the plane, be prepared to carry your bag (full of work) and childs bag (full of nonsense) while yelling at your child to get off the heels of other passangers, to slow down, to speed up and to make good choices in general. This includes not touching the switches that detach the runway from the plane.
4) Ignore everyone ignoring you hoping that your child doesn't want to sit in their aisle. Guess what! We don't want to sit with you either!
5) When you offer your child a peanut on the airplane, be prepared to ride with it in your shoe for the rest of the flight. In fact, instead of offering the peanut to the child, just place it in your shoe instead.
6) Don't wear a watch. Time doesn't exist on an airplane when traveling with a child. It will be the same time the entire flight (time to remember your birth class breathing techniques)
7) Prepare for your child side arm to resemble Brad Pitt's arm from fight club based on the number of times you will be poked for more: fruit snacks, tootsie rolls, crayons, ipad, books and of course for no reason at all.
8) The child will always want to go to the bathroom on the airplane. Always. Strategic move: Whisper in their ear that they should ask your travel companion to take them. If you are traveling alone with a child, have mercy on your soul.
9) Passing the time: Guess how many times you will say: "Sit still and stop touching the seat infront of you". (Wrong: More times then that)
10) When the arrival chime dings and your fellow passangers become absolute cagged rabid animals leaping up and grabbing their belongings when there is absoutely no where to immediately go, your child will be inspired to lose his shit and want to jump on the seat, head butt you and ask 700 questions about getting off the plane.
Finally, repeat #3 and just enjoy your vacation. They are only 4 once afterall :-)