Those are tropical and humid cities. Weather won't be much different between them. You don't need warm clothes for the summer, a light jacket/windstopper might be good.

Not sure whether you are traveling for leisure or business. You will be in 4 cities in 14 days don't need to bring lot of clothes so 3-4 set of clothes should be adequate. Clothes are inexpensive in Bangkok, Shanghai and Beijing.

You didn't mention whether you are male or female so clothing needs will be very different

Try to to search the web for "travel packing list" etc.

http://travelindependent.info/whattopack.htm