Believe it or not, traveling during Southeast Asia's monsoon season can be a good thing for travelers: hotels and flights are cheaper, and less traveler volume means you share the tourist trail with fewer people going the same way.
If you're aware of the downsides of traveling in the rainy season and have prepared for them, there's no reason why your September jaunt through Myanmar or Vietnam can't be the best (and best-value) trip you'll ever have. Start preparing for your Southeast Asia monsoon season trip by consulting this packing list.
Rainwater creates pools of stagnant water in the tropics, allowing mosquitoes to breed and proliferate. Tourists traveling through monsoon season may be susceptible to catching mosquito-borne diseases like malaria and dengue fever if they don't take adequate precautions.
Pack a tube of DEET anti-mosquito spray like Off! Deep Woods Sportsman Insect Repellent.
Your regular windbreakers are no good here, if you don’t want to be walking around a soaking mess. On the other hand, there's no need to overspend for a fancy rain jacket that'll only do a poor job of keeping the water out of your clothes. A plain PVC raincoat packs light and provides ample rain cover; it doesn't feel too warm, either.
Alternatively, you can get a travel umbrella that fits into your handbag or knapsack when folded. In the months between July and September, you'll likely need both a raincoat and umbrella to keep you somewhat dry.
Traveling in the humid tropics during monsoon season calls for clothes that dry easily, but feel cool when worn. While cotton clothing is cool, it absorbs moisture and takes longer to dry.
So leave those denims at home; you're better off with polyester-blend clothes that have all the positive properties of cotton while drying faster, even in humid air. Synthetics also tend to take up less room in your luggage, providing you with more space to pack.
If you're traveling during the monsoon season, leave your fashionable leathers at home; you'll want shoes that make it through the wet roads without too much damage. Waterproof shoes are an option, but they'll weigh too much and are no good in a flood. (Besides, they're just as good keeping water in as out; imagine how stinky your sweaty feet will be once out of those boots!)
Bring sandals instead; as long as you keep them out of serious floods, you'll do all right—just dry your feet when you get back to your hotel room. Don't walk outdoors in your sandals if you have broken skin on your feet, though—that's asking for trouble.
Don't face the monsoon season without some protection against germs. Bring a tube of hand sanitizer to rub it on your hands after coming into contact with damp surfaces. If the water's looking iffy, take a SteriPen water purifier to treat your drinks with. Both will cut down on the risk of contracting cholera, dysentery or other nasty bugs.
You'll find your bag contents can get all damp and mushy in the humidity of the monsoon season. Your electronics and camera equipment are particularly vulnerable to the high moisture content in the air. Fight humidity in your luggage with packs of silica gel—these little pouches suck up ambient moisture and keep your bag internals dry even in high humidity.
The monsoon season brings more frequent power outages, particularly in places with un-robust electrical grids. Don't be left in the dark - bring a small flashlight with you. Your travel flashlight should be waterproof, stingy with the power it uses, and use regular AA batteries (something you can buy even in the boondocks).
Flashlights like the Energizer high-intensity LED flashlight fit the bill.
Polyethylene bags are useful in isolating your wet clothes from your dry ones, or for keeping your clothes dry in less-than-waterproof luggage. Bring regular polyethylene garbage bags along with you; as you travel, wrap your clothes, documents , and electronics in them, and pack in your luggage to keep them dry.