How exciting! I've been to Hong Kong, but not out into the countryside. What a great adventure!
The best all-day shoes and backpack for you very much depends on what feels good to you. I'd recommend heading to an REI or similar store where you can actually try on and try out equipment before you buy. Opt for as slim a pack as you can fit your stuff into - in the city the streets are always crowded, as is any form of public transportation, and big backpacks are a major hassle in crowds. You need one you can comfortably swing off and hold in front of you when necessary. If you'll be wearing the pack all day, consider one with padded shoulder straps and a chest or waist strap to help distribute the weight more evenly.
Another thing about shoes - if you'll be going in and out of private homes, you'll be removing your shoes. You need shoes that are easy to get in and out of. Velcro is your friend in this case.
A few just-in-case items to pack - Immodium tablets (I never had tummy issues, but it's better to be prepared), antihistamines (you'll be meeting all kinds of new foods, bugs, and plants, and unexpected allergic reactions, while rare, can happen), hand sanitizer, and some female sanitary products if you're going to be getting a visit from "Aunt Flo" while you're there (you can find them in the city with no trouble, but out in the countryside, who knows?)
You might also want to take a supply of something typically American that you can hand out to people whom you'd like to film or photograph - a friend of mine who is a professional photographer handed out dollar bills or Hershey bars to people who let her take their pictures. State quarters, postcards from Indianapolis, or hard candies of some kind would probably work, too.
If you're not good at using chopsticks, take your own fork in a small case.
Have fun!