As long as you are on a tourist visa and doing nothing to attract undo attention, then you should be fine. Obvious blunders would be a T shirt about "Free Tibet," or something similar insulting to your Chinese hosts. I have carried my duty free two liters right through customs.

Smile, exchange some currency before customs, and proceed onwards. You will enjoy China best if you see some real rural agricultural villages off the tourist trail as well as Beijing and Shanghai.