I have flown alone several times.
1. Have cards or papers with notes for the people (flight attendants, ticket desk workers, security line personnel, gate attendants).
Have the cards say that you have an Autism Spectrum disorder, perhaps things you need help with. I have cards saying I may have trouble speaking. I fly Southwest Airlines where you are not pre assigned seats, I ask to pre board (get on board before everyone else to see the plane, arrange myself, and not be rushed). I also ask for a seat in the very back by the window as I feel safer in a corner, but you may want to ask about other seating option.
I have one just for security to allow me to by-pass the long line, I get taken to the front.
I have cards if I become disoriented and need to be escorted to my gate. I have cards if I have a layover to ask for help to the next gate.
2. Sensory items, power plugs, batteries, portable charger, stuff to do.
Plane rides are long, there is lots of waiting and sitting. I use my ipod touch for most everything (except phone calls, but I avoid those anyway). I make sure I have a charging cord with me, sit by electrical outlets while in the airport, and have a portable battery based charger if it dies mid flight.
I also use isolating earbuds that help protect me from the ambient sounds and speaker based announcements. (Another reason for cards, it notifies people that to get my attention they need to wave a hand in my face, and that I may need someone to get me when boarding comes).
3. You also may want to take an anti-anxiety med before leaving if needed. Also you can talk to the flight attendant and captain if you are afraid of the flying itself, and they can help reassure you.
Also not all domestic long flights play a movie.
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