Adding to the above suggestions, I particularly suggest getting:
1) The Cho Chikun Life and Death Dictionary (the one illegally translated as "All About Life and Death")
2) The Weiqi Small Dictionaries can be good for the problems:
http://senseis.xmp.net/?WeiqiSmallDictionarySeriesI have the endgame book and it contains a number of 11x11 problems that I haven't seen elsewhere.
3) The Korean Speed Baduk series is available as "Sucheng Weiqi" (速成围棋) in Chinese. In addition to Vol 1-12 (which have been translated into English) there are some follow-up volumes (which have not yet been translated.) Vol 1-12 didn't have solutions when I was in China last year but the later volumes do have answers in the back.
You probably know this, but Western credit cards generally won't work in Chinese bookstores, so bring cash when you go shopping. If you run out of luggage space, you can always mail yourself a box of books -- if I remember correctly, surface mail from China isn't all that expensive.
I'd be surprised if you found slate and shell stones at a price much lower than ordering directly from Japan (luxury items in China are not cheap.)
Have fun on your trip!