Keeping your clothes dry

It might seem a basic thing, but trust me, I have seen many of my co-workers getting their sleeping bags and clothing totally or partially wet while staying in a camp during the emergency operations after the Typhoon Bopha in the Philippines.
During the rainy season, it is actually raining all the time! Even though the weather might seem sunny, it can quickly change and a huge waterfall can come from the sky at any time.

After the second time my things got a bit wet due to rain coming inside the tent, I looked for a big trash bag and put everything inside. It is not even necessary to close it very tight, as it will never be submerged (we hope)
This kept my clothes and electronics clean and dry during 6 weeks living in a tent during rainy season.

a big trash bag is light, cheap and easy to acquire

Not only in tropical weather a plastic bag is useful. While camping out in the sudanese desert for the first time I got fine sand (dust like) all over my things, including inside my sleeping bag and even inside my backpack. After that I always carry a big trash bag. It's a simple solution that simply works.