I just went to the 1st phase of the canton fair, if the 2nd phase is anything like the 1st one here is a guide to food and drink at canton fair.

Basically, water and drinks are available are available through out the trade show buildings. The choices are pritty much the same for all the outlets but that's a bit expected. Soft drinks, beer, bottled tea and water are the usual items.

Pazhou complex
McDonalds
Fast food
Cafes

Liuhua Complex
Restaurants
Cafes
Chinese lunch boxes
Chinese Restaurant

Western option is fairly lmited (although available).

I didn't see starbucks.