Packing Tips
Packing for your first trip to Southeast Asia can be a little challenging. For the most part, you can use common sense and forethought. The most important thing to remember is that, no matter where you go in Southeast Asia, or when, you'll be in the tropics, where it will probably be a lot hotter and more humid that what you're used to. So, with that in mind:
Pack "light" - cotton or silk fabrics in casual, breathable designs. No matter what time of year you visit, you're unlikely to need a jacket, or even a sweater.
Even though the weather may be hot, you should not assume that you can wear shorts all the time. Many of the main tourist sights in all countries require that you be "properly dressed" in long pants or skirts for entry. The same is true of tank-tops. Even if you're planning on spending all your time at the beach, you will still want to be able to cover your legs in the evening to help keep away the mosquitos that are prevalent everywhere there is water.
If you're planning an extended vacation, you can plan on doing laundry while on your travels. There are few self-service laundries anywhere in Southeast Asia, but you'll find full-service washing, even at hotels, to be quite reasonably priced.
Bring sun-tan lotion, after-sun treatments and other minor first-aid products with you. These items, generally imported, can be quite expensive when purchased in the region. However, pack them in your checked luggage, since the ICAO liquid, aerosol and gel rules apply at most airports around Southeast Asia.
Lock your checked bags. Unfortunately, pilferage is still a problem at some airports, as is smuggling. If traveling to or from the USA, you'll need to use "TSA" locks that can be unlocked by airport security if needed. For outer pockets and emergency use, I generally have a handful of plastic cable-ties that can be cut off and discarded. You can find these at hardware or electronics stores where a large bag of 100 or more will set you back a lot less than the cost of a "TSA" lock.