Just got back home from a trip where I used the blanket Kevin recommended. Used it constantly....love it! Dh and I can actually share it on the plane, then in hotel rooms we like to have a really cold room for sleeping ...Oh, but I stay up late and Dh gets up super early, so we each use it then to stay warm in the room. It's super thin but really keeps the heat in your body.
I'm usually a 'frugal' kind of gal, I've had different travel blankets in the past that I spent under $10 on, but this one is well worth the money. Here's a link to it through Travel Smith...bonus, accessories (which it is, are shipping free right now).