Airports, Airplanes

One of those "Alyssa answers a question" things:
iamthegps posts:

On April 25th, I’m traveling to Costa Rica with a school trip and while I am very much looking forward to it, I’m not so much looking forward to being in an airport for the first time, much less two airports within a couple hours of each other. So I decided to search the internet for advice on how to manage getting through airports when you’re autistic and I found exactly nothing. All I could dredge up was a couple of articles on how to travel with your child and one about how embarrassing it was for somebody when her kid had a meltdown on the plane. Nothing about how to deal with crowds or TSA or getting your tickets or anything (also known as advice I’d really appreciate being given). So yeah, any advice would be greatly welcomed, and thanks in advance.

I've studied abroad four times, the first and third times I did my traveling/airporting alone, with the second and fourth done in school groups.
When alone, you need to actually pay attention to stuff. With a school group, one person will take care of finding all the things, so make sure you don't volunteer to be that person, then bring whatever you use when you want to tune out the world and do so. Make sure one member of the group is aware that you are tuning out to the best of your ability and ask them to make sure you don't get left behind. If that is the case, skip the next several things because someone else is taking care of it for you. They may ask for your passport, and you may need to follow them for one piece if you are checking a bag.
If you're alone, just arrive early enough that you can take a few tune-out breaks if needed.
If you can pack everything you need into your carry-on allowance, you can do electronic check-in for most flights, even many international flights. This reduces the need for interacting with people, but requires packing very light. It can be done- I packed for two months in China within my carry-on allowance, but that doesn't mean it's easy.
There will be signs pointing to where things are, check-in is generally near the entrance. Read the signs on the check-in booths, because different booths are for different airlines.
Use all rolling suitcases except for a possible backpack. Just do it.
Make sure that at least one rolling suitcase is packed in a way such that you can sit on it. There will be lines you need to "stand" in, and this suitcase is your new portable chair.
Bring communication cards with things like "where is the bathroom?" and "where is security?" and "where is check-in?" just in case.
Bring entertainment. Delays are a thing. I wound up with an eight hour delay alone in Toronto when I was sixteen, and I have never traveled without laptop, book, notebook, and pen since.
Know what the contingency plans are for overnight delays at middle points if you have to transfer. Knowing what happens if the first thing goes not as planned is helpful for avoiding meltdowns and also because you don't want to sleep on a hotel couch in the basement when a six hour delay on one end (Shanghai) gets you stuck (Toronto again) alone in a country that won't let a minor get a hotel room alone. It is not fun.
Don't use Air Canada for international flights unless you have time for major delays.
If you can smile at security and ask how their day is going, they will be nicer to you. (Might only apply to white and white-passing.)
If you pack too light (backpack only, for example), people get suspicious and might pat you down. Have a carry-on suitcase in addition to the backpack, because patdowns are not fun.
There are metal detectors, which are not optional if that is where they send you. There are also millimeter wave things and X-ray things, some of which you may refuse, but you will be patted down if you do so. If you are sensitive to touch, don't refuse.
Noise cancelling headphones are your friend. Or earplugs. Assuming you can use them, that is.
Some people can sleep on planes, some can't. Go ahead and try, but do not base "getting enough sleep" on the assumption that you can unless and until you have experience that says you can.
If this is your first time flying, try to get a window seat. It's worth it. I've flown a lot, and I am still a nose-to-the-window flyer. It also gives you control over open/closed in case of airsickness.
Don't ask for details about how security works. You can (and should!) look them up online beforehand, but asking while there will make people suspicious. Suspicious TSA (Transportation Security Administration) agents give pat down searches.
Do not bring a full water bottle through security. They will throw it away.
You can bring an empty refillable water bottle through security, though.
You can also bring food. Bring a comfort/stim food.
Have stim toys in your carry-on, preferably in the smaller backpack that you put under the seat in front of you so you can access it during the flight in addition to while in the airport.
At security, they will make you take your shoes off. Wear shoes that you can take off and put on quickly and  easily. They will let you keep your socks on, so wear socks if you don't want to be completely barefoot for that part. If your socks having touched the (admittedly kind of gross) airport floor at security will bother you, pack a spare pair of socks in an easily reachable spot in your carry-on.
Liquid that you can bring through security is limited. If you aren't picky about shampoo or won't be going for long enough for a 3oz container to run out, this isn't as big a deal, but otherwise, make sure it is in a checked bag. If this and/or sunscreen is the only reason you need to check a bag, you may be able to stick to carry-on by asking a friend to put these two things in their bag and offering to carry an equivalent amount of stuff of theirs in your bag. (That won't work travelling alone, unfortunately.)