Sounds like fun. I don't know anything about kayaking in China, but I did visit there briefly. I can tell you I was initially nervous about getting sick eating stuff from streetside vendors and uncooked fruit, and such, but the guy I was visiting there had a laissez faire attitude to the whole thing that I got into. So I ate just about anything and anywhere so long as it hadn't touch the ground and I never got sick. I thought one of the best parts of being in China was the food - really good and super cheap and you can pick up some great stuff from streetside vendors for almost nothing. Fruit actually tastes like fruit there. As for eating fish head soup and intestines and such, I say go for it - all part of the experience (although eating endangered species like turtles is not cool, even if they do make you sexually virulent) That said, I heard some stories of questionable sanitation from places in Tibet, so if you're in Western China, which it sounds like you might be, maybe you should try to get a look at how clean the hands are of the guy preparing your grub.
Also, I found the Chinese didn't have much respect for the ground. I suppose it will depend where you are, but in the cities there was a lot of spitting, children urinating, and garbage thrown on the ground. Main point being, don't lick the ground, and most hotels have little slippers for walking around your room - use them.
I found Chinese culture to be really foreign. Be prepared for behavior that you might find rude such as unabashed staring, pushing and shoving, and general disrespect for personal space. Unfortunately as a foreigner you will be targeted as a person with lots of money who should be ripped off (the government seems to even encourage this behavior). Expect to get ripped off, but try not to. Also, most rules like no photography, no food or drink in such and such a place, etc. seem to be generally ignored. However, it is a police state so don't get on the wrong side of the law, but if all the locals are ignoring the rules, you're probably safe to follow suit.
The card is a classic piece of advice for traveling in places that don't use our alphabet (really annoying, wish these guys would get with it). I assume you'll be accompanied by someone who speaks the language, but if you're venturing out on your own via some mode of transportation that makes getting back on your own unclear, it's not a bad idea to carry a card with the name of your hotel on it.
Hmm, otherwise my advice is be open minded, don't act like a spoiled American brat (i.e. don't act like Bill O'Reilly) and bring back some cool paddling pics and stories.