For clothing, my top goals when traveling are comfort and efficiency - then style. When all three are combined, I've found travel-apparel gold. Leggings, a long cardigan, flats and a scarf is one of those outfits.
I know there is a whole "leggings as pants" debate. People take sides, it gets ugly. But I have to say, I am a fan of the simple black legging or jegging when it comes to plane flights. There are not as sloppy as sweats and are far more comfortable than most jeans. They are also stretchy - perfect for all that contorting in your seat to get comfortable before you can sleep.
Keep colors neutral throughout the outfit, but feel free to mix and match them. Wear a basic white tee, long sleeve for this season, under a thick knit cardigan. I like to wear a thick marled wool cardigan from JCrew or a DKNY cozy, but I also quite like this one in a narrow cable knit from All Saints. Here is the caveat about leggings as pants - your top must cover your butt. That's why I recommend a long cardigan such as this one.
In terms of accessories, layer with a circle scarf which can double as a pillow on the plane. Scarves are also great to hide the wires of iPod earbuds so you can keep listening to music even after you've been warned to turn off all electronic devices. Wear flats - simple, comfortable black ones are ideal in this case. They will easily slip on and off when you go through security. And use this LeSportsac metallic carryall as your carry on - both stylish and functional.
