Usually I wear my Witchery maxi dress - it's knitted, so it's nice and cool; it's really soft, so in technical terms, it's like wearing a blanket; and it's still stylish enough so that I can wander out the airport (or, in my case, Bunbury train station) looking relatively put-together.
I put together some outfits on Polyvore that I think would be awesome from anything from a two hour train ride to a twenty hour flight to Paris:
Do these pants look like the most comfy things ever or what? Wearing an outfit of muted tones would be very soothing for a red-eye flight, I think. I absolutely adore this T-shirt. This outfit makes me think of a girl on a plane scribbling furiously in her notebook and reading book after book after book.