What do I pack for a trip ti Zin Jiang from September 20th - October 4th?

You must refer to Xinjiang, don't you? Well, it will be a little cold at that time, though the sunny days would be the majority. The highest temperature could be around 20C and the lowest temperature may fall to 7-8C. So you'd better prepare one or two thermal clothes like thinner down jacket.

Don't worry! The bottled water and food can be safe there.