Outdoors it will be hot and humid. You'll want lightweight clothing. Shorts and tank tops are okay for the beach area, food stalls, and other casual places. Indoors, especially during the IDC, you might find it air conditioned and rather cool. All through my IDC I wore trousers and long sleeves anytime we were in classroom sessions. If you find the time to do anything other than the IDC--wearing skimpy clothing in a wat is inappropriate. Beyond that, if you find you need more than what you've brought, just go to the market and buy something.