I have found that we tend to keep the air conditioner set colder and run it more often in hotels that we do at home, which dries the room out quite a bit - even when it's unbelievably humid outside. Last year I started traveling with a humidifier and I was shocked at the difference it made! For the first time, I came home from a vacation without a sore throat and sniffles. We drive to Florida, so it's easy for us to throw the humidifier into the car. I'm not sure I'd take it when flying, but I'd certainly try Dani C's suggestions. I've also started putting a cup of water in the car cupholder when we travel, since the air conditioner on long trips in the car always gives me a sore throat, and that seems to help as well.
ETA - Another plus I've found about the humidifier is that it works great as a "white noise" machine. It helps me not focus on any noise that might be coming from outside the room, or any snoring that might be coming from inside the room! Before we started using the humidifier I was using the TV to drown out any noises, which the other people in the room didn't particularly enjoy.