I bring a good book/my kindle, my ps vita, and an external battery.
I'm pretty fortunate in that I can really easily sleep on a plane, so most of the flight I sleep, this sometimes helps when changing timezones.
If you’re in the UK, not sure if other countries have this, then pay for express security. It’s around £5 and you can skip the inevitable mile long security queue (looking at you Birmingham International) and get through much faster. Money well spent.
give yourself plenty of time. It's better to be bored for 30 min at the gate than running through a terminal trying to catch your flight
be ready for security, try to pack so it's easy to do things like get your laptop out and so you don't need many bins. If that's not possible, just be calm and organized
tuck stuff from your pockets into your bag before security (wallet, keys, phone, etc.)
avoid belts, hats, heavy shoes (things they'll make you remove)
on the other side of security, move your stuff to the side when packing back up (there's often a table you can move to)
bring a water bottle and find a water refill station after security so you don't pay a ridiculous amount for water
if you can bring your own (non-smelly) food for the airport and plane, assuming you're not getting airplane food, to avoid the ridiculous prices for food at the airport
be close to your gate 45 minutes before your flight. Boarding will likely start 30 min before, but be there for announcements and in case they call your name
before boarding, grab small things from your bag you know you'll want, like your headphones, charging cable, etc. and put them in your pockets to make it easier when you get to your seat
there are likely people in front of you and behind you. Treat the seat in front of you and your seat back with respect. This includes when you go to lean your seat back, do a courtesy check
keep your elbows in
make sure your kids do the same, e.g. they aren't kicking the seat in front
don't wear sandals
don't put your feet on the arms of the seat in front of you
keep your voice low
don't get drunk
shower and brush your teeth before you travel
don't wear heavy scents (e.g. perfume)
during the taxi to the gate, gather your stuff and check the seat pocket carefully
let people into the aisle and off the plane in a respectful manner, don't crowd forward
It's generally unsanitary, especially when using the toilet. Often it's smelly, even if you don't realize it. You'll be in crowded spaces and risk getting your toes injured.
If you have a tablet, bring that for entertainment. Or you can use your phone. All of the bigger subscription services (Netflix, Hulu, Prime Video, HBO Max, Disney+) have a download option for movies and shows, so download an array of things you're interested in to your phone or tablet ahead of time. And some airlines have their own library of media for free on their wifi, without having to pay the outside internet fee. Make sure you have the airline's app downloaded.
The best seats on a plane (outside of 1st class, obviously) are the 2nd exit row seats, if your plane has 2 rows of exit. Most leg-space anywhere, but the 1st row seats can't recline so they won't block the 2nd exit row.
I can sleep on planes, so I purposefully only get 5-6 hours of sleep the night before and use the plane time to catch back up on sleep.
Your armrest can fold up, there's a little button underneath it towards the back. Push that in and push up the armrest. Good for when you have an aisle seat for getting in/out, or if you don't have someone sitting next to you.
If you're in the US and have to fly a few times a year at least, TSA precheck is very much worth it. Even longer Precheck security lines go pretty quick. Your job may even pay the fee for you, or some airlines you can pay for it with miles.
When I land, I just sit there for a bit and let everyone else get all hot and sweaty trying to get their carry on luggage first and get off the plane first. There's no real rush, and if you have checked in luggage in the hold you're going to be waiting for that anyway.
I'm a hand luggage only kinda guy. Easy on, easy off, no faff with the conveyor at the end.
I'm a pretty good flyer anyway, so I just make sure I'm wearing something comfy, my AirPods are charged and I've got something I want to listen to on my phone. Depending on the length of your flight, I think it's always worth having a bottle of water to bring on from the airport, or buying one on board. It can get dry in the sky!
I have debated buying an iPad recently, not for flying/travel but just general usage - however, I think an iPad would be a great addition on a longer flight. Pop a movie on!
Water is a really good shout, but instead of buying a bottle at the airport (which can annoyingly expensive) you can bring an empty refillable bottle and fill it up after security!
I have mobility issues so I take a length of paracord or two shoelaces tied together to double thier length in my "personal bag". I tie a loop on one or both ends.
When I sit down, I haul it out, run the loop under a strap on the bag, then run the free end through that so I now have a line on the bag I can use to pull it up to myself. I stuff the free end into the seat back pocket and try to tuck it away so a flight attendant doesn't need to give me a hard time.
Then the personal bag goes under the seat ahead of me and I can reel it in whenever I need something.
Set your meal preference. I usually choose "Asian Vegetarian". That guarantees you a (somewhat) tasty curry and you'll also be served first.
If you're travelling to somewhere with a significant timezone change, prepare beforehand. Start shifting your body clock about 1 hour per day. Most importantly, shift when you eat your meals - that seems to be the key for me.
Unless you are flying business class or higher, there's no real way to get a good sleep on a plane. All the gadgets in the world won't help. Get a thick sleep mask and some earplugs and hope for the best.
Once the seatbelt sign is off, take your shoes off. You'll feel a lot more comfortable. Put them on if you go to the toilet though!
If you're renting a car: when you land head straight to the car rental desk. Luggage takes a while and the lines for car rental can get long. If it's a short work trip, skip checking in a bag and only bring a carry on, way less of a hassle
Edit: for work trips especially, people drink and eat way too much when they're on the road. Definitely look up some fun things to do in the area that don't involve eating or drinking. You'll have to get comfortable doing fun things by yourself if your work requires travel.
Edit2: if you're the one booking the travel and hotel, get an expedia account and book it through them. The points really add up and they'll subsidize fun vacations
If you carry comfort stuff for your car I'd recommend taking that stuff for the plane ride. A blanket and a neck pillow really make all the difference. Plus make sure you have a good portable battery.