I traveled in Laos. To be culturaly correct pack long skirts! They are not only required to enter some temples but will afford you added respect and safety all over the country. I personally love the long skirts carried by Patagonia ...sturdy, simple classics. They are also cool and comfortable for trekking.
Sophia, Tokyo, Japan

I always dress conservatively in any country in Latin America. I prefer to wear dresses in dark blue, gray or black along with comfortable mocassin type shoes with flat heels. You'd never catch me in shorts, sneakers, birkenstocks or a fannypack. This worked well for me as I usually was not aproached by street vendors selling items to tourists and was able to tour local markets quite undisturbed. I also make a point of dying my ash-blond hair a darker color before I go to Latin America and that may help, also. I do not use a backpack unless I am on a jungle excursion but rather a plastic shopping bag which the locals also use.
Erika, Spokane, USA

For what to wear in London, England click here.