Because the new technology is adopted by the airports for the safety check of the passengers by air, those high speed films like 400 might be damaged by repeated X-check. Take them out of your luggage before the luggage goes through the check. Taxi in China, just like other countries', charges by meter. If you still are not sure the for the accuracy of the meter, ask someone, for instance, the bell boys of the hotel who might know about your destination. You don't have to leave tips on the table in the hotel room before you are out for sightseeing.
China is a country with very tough rules on weapons.
If you have bought a knife as a souvenir, remember to keep the receipt from the gift shops, and lock it in the checked luggage throughout the trip. Nevertheless, the safety of the foreign tourists to China is guaranteed by the government, even at the situation when the relations between the countries fall into a temporary low. Please check the latest statement of the travel tips and Announcement by the US State Department. Hold you hand-bags in the front when you are walking through a crowds. Always ask someone you know to keep eyes on your belongings while you are temporarily absent from it.