Sounds like a fabulous trip.
I'd second Mo's suggestion of a cotton skirt and flats worn with a variety of tops. Personally, I prefer a straight-cut, knee length skirt in a pattern, or deeper color, so I can sit anywhere without worrying about marks. Although I like them on others, I find floaty, longer skirts don't work as well if I'm active or if the wind is blowing.
I bought a pair of these Ecco shoes in a light grey earlier this summer and they have been my go-to casual shoe with shorts and skirts this year. Practically indestructible and enough support to let me walk anywhere. These are fairly sporty, but Ecco has other styles that are a bit more dressy.
http://www.zappos.com/ecco-lite-skimmer-ii-misty
And don't forget a cute, summery hat to keep the sun off your face!
ETA: Having said all that, my best friend recently spent time in Thailand, Vietnam, and Cambodia and, in almost every picture, was wearing a short-sleeved, white!! , cotton dress with a full, floaty skirt that came just below her knees. She wore it with a wide, woven leather belt, similar-toned leather sandals, and a natural-colored, wide-brimmed straw hat. She looked amazing in every picture!