1) Fountain drinks and ice consumption at the western-branded restaurants like McD's and KFC are safe. Water supply does not come from tap but from bottled, and ice comes from purified ice factories. I will also use ice in drinks from "better" restaurants. In local dives and very small town restaurants, I buy canned soft drinks from the cooler, and use a straw. Cold beer is always OK. (Actually even warm beer is OK just yucky.) Bottled water is everywhere. Tap water is not OK anywhere (even though in cities like Beijing, it is treated, there are still too many potential breakdowns in the treatment and distribution process to trust it).

2) I personally avoid lettuce and uncooked vegetables on sandwiches and elsewhere, since I can pretty much guarantee they will have been incompletely washed and then under tap water.. But then, I do this even in the USA and developed countries as well. I tend to avoid salads unless prepared at home, or at very particular restaurants. Five-star hotel catering should be above reproach, but often isn't.

3) Airline catering should always be suspect. Use same protocols as you would in ground-based restaurant. I avoid: any cold seafood such as seafood salad (actually on any airline anywhere, these days), cold salads with raw veggies (ditto), ice in drinks (though that's probably safe).

FWIW, I've lived in China for over 10 years, and have NEVER had a gastrointestinal illness at all. It is not inevitable that one will get sick on a trip, you just have to use common sense. A cousin once got horribly ill gobbling from the sushi bar at a Nanjing upscale hotel. Tried to tell him this wasn't a good idea but he wouldn't listen. His punishment for not listening to the Wisdom of Jiejie was a night in the bathroom praying to the Porcelain God.