As I write this, members of the Legislative Council are on their way back from Shanghai. For one legislator, however, the airport was the only place he visited in Shaghai. During the immigration process, his luggage was searched and customs officers to him that he would be denied entry unless he surrenders "sensitive" items he brought along, including a T-shirt, on which it says "Tiananmen Mothers Campaign", he wore, and letters demanding release of political prisoners and opening Chief Executive nomination rights to all electors. As one cannot official define what items are "sensitive", this incident made me wonder if there is a secret list of items which one cannot bring into the Chinese mainland. If such list exists, it may contain the following items
Milk powder: bringing milk powder into the country would be a not-so-subtle reminder to Chinese officials that milk powder produced in China is not safe and that the authorities have not been diligent in shutting down manufacturers producing sub-standard milk powder. (This may apply to other food products, diapers, clothing, and blankets as well.)
Merchandise showing a ferocious lion: pictures of ferocious lions and lions chasing down prey would run counter the President Xi's message that China today is "a peaceful, kind, civilized lion". Banned merchandise include, but not limited to, products bearing the MGM logo, Detroit Lions (NFL) merchandise, cars manufactured by Holden.
Products bearing the name Vladivostok (in any language): Such products would remind Chinese people that the Qing Dynasty willingly surrendered the territory and that the current government is doing nothing to reclaim a piece of "Chinese territory since ancient times". Such products may also incite people to develop anti-Russia sentiments, something the government prefer not happen as it would mean the country is surrounded by "adversary forces".
Kit (jersey, shorts) of foreign national football teams (not applicable to actual teams visiting China):. While China is now a world power in individual sports, the country's track record in team sports is less than stellar, football in particular. Showing up in a kit of foreign football powers would make Chinese football fans wonder why the country is incapable of finding 20 or so decent footballers capable of playing cohesively. (One problem in enforcing this is what happens when someone is caught possessing a made-in-China replica.)
Phones (and tech gadgets) designed by foreign companies: Chinese officials often carry the mantra "enemy's undying will to kill(destroy) us". By carrying along phones (which may be embedded with GPS tracking devices, wiretaps, voice and data recorders) designed by companies from the US, South Korea, and Japan into the country, the owner may compromise the country's security by leaking state secrets to enemies abroad simply for using the phone to make calls and text.
If the above list does exist, the customs officers may be so busy searching for "contraband" items that truly dangerous items may slip through. No worries though, as this just means the government can create more jobs and divert more money to China's weiwen (stability maintenance) industry.