Guangzhou and Georgia has practically the same weather, I guess that's why I wasn't in too much discomfort there, I work outside here in Georgia year round 8-14 hours daily doing maintenance on ready-mix concrete plants so I am accustomed to hot and cold weather! Wear loose-fitting light colored " cotton ' clothing, a hat, and keep a water bottle/sports drink with you to rehydrate with and you should be fine. I would recommend eating small meals during the day and avoid fatty and greasy foods that will weigh you down. As a word of caution, ALWAYS keep some toilet tissue in your pocket/man-bag just in case the outside meal does not agree with you and you have to brave the public toilet
which usually has nothing even resembling paper within arms reach!
I would recommend taking an unopened package of Amodium A/D with you also to help with trots if you get them!
The trick to eating in a place you have never been is to watch where the locals gather to eat, they usually are a good indicator of safe places to eat. The sidewalk vendors for the most part should be avoided like Gerry mentioned earlier, but normally the locals only eat where they feel safe so you should follow suit. I also recommend getting some lemon scented moist wipes, you can wipe your face or hands and feel refreshed at the same time. One other thing that you might watch out for is eating too much sticky rice, that stuff will stop up a hydro-electric plant turbine so be careful.
Good Luck and Best Wishes
P.S. Watch out for Pick Pockets , they are everywhere