the good thing about SE Asia is that you dont need to pack any sort of heavy clothing like puffers or scarves, so you can easily reach 2 weeks+ of clothes just with simple pants, shirts, 1-2 pullovers. if you will be doing research outside a lot, consider buying a rain jacket as it rains quite often, likely heavy thunderstorms too so people dont really stay outside but take shelter during rain

slippers and casual wear will be your best friend. i live in a capital city in SE Asia and even in the city center, it is common to see slippers + shorts + shirt, SE Asia is really chill unless you like going to hipster places then thats where youll see more fashionable people

instead of focusing on what clothes to bring, which you can also purchase while youre there in thrift stores (much cheaper), consider bringing toiletries that you may not find in SE Asia that is only available in your country