I have also gotten very good at packing light. I can do a 10-day business trip across several countries (and several vastly different climates) with a rollaboard and a knapsack. I always go with basic black as my staple and simply vary the types of shirts I bring. So I bring 2 pairs of black pants, several different white shirts (t-shirt, long sleeve shirt, turtleneck), and 2 bright-colored jackets from Chico (suede-like material that is super lightweight and doesn't wrinkle). I may also throw in a lightweight black cardigan. This way I can vary my outfits across weather with just changing from a t-shirt to a long-sleeve shirt. I wear on the plane a pair of black pants from Lucy (which ends up looking fine for dinners or for sightseeing), a white shirt appropriate for the weather and a fleece half-zip. I bring just one pair of shoes (Merrell's) that can dress up or down. I pack underwear (travel light ones from Soma that I love and just discovered), socks, and bras into ziplock bags and squish all the air out so that they are supercondensed. I bring a second bag to shift dirty ones into. Throw in a pair of pajamas, my bag of toiletries, and I'm good to go. I am fine with re-using a shirt. Finally, I have a pair of super lightweight thermal long underwear that I put in if I'm heading someplace cold. I can layer it under black pants, it doesn't show, keeps me toasty, and takes up almost no room.

Into the knapsack goes a book for the plane, my iPod, a small purse to bring to meetings, and all my chargers/paraphenalia. Laptop goes into outside pocket on my rollaboard so I can wheel it around and not carry it on my back. I transfer it into my backpack at the last minute when I board a plane so it goes under the seat and is accessible. Also it makes it so my rollaboard isn't too heavy for me to lift and put overhead.