An IT Security focused blog is not really the right place to give out travel tips, but it's my blog so here we go.
I've received lots of great travel tips over the years but one of the best ones was for any flight you go on, especially long haul flights was:
You can bring an empty bottle with you through customs and then fill it up and drink plenty of water on the flight.
There are many bad things about long flight, but I feel like most of these things are exasperated by being dehydrated. Airlines give out small amount of water in tiny cups infrequently. Also I think1 that the air-conditioning in planes is set to a very low humidity which drys my skin.
Even through you can't bring more than 100ml of liquids through customs you can bring an empty water bottle and most airports will have water fountains (usually located near the toilets) that you can use to refill your bottle.
Filling up my trusty water bottle at Leonardo da Vinci–Fiumicino Airport, Rome, Italy
I know that should be obvious that you can bring an empty bottles through but I've seen a lot of people throw out bottles at customs rather than just emptying them. Alternatively you could just buy a bottle of water after passing through customs but if your travelling a lot that's a lot of wasted bottles and do you really want to pay $5 for a small bottle of water?
I know nothing about the air-conditioning settings of planes, or it's effect on skin, it's purely anecdotal, and could be completely wrong. ↩