what can one buy and take home?

Generally speaking, souvenirs are allowed to take out of China. You can take most of the things out of the country, except for the following items.
1. Any kind of weapons.
2. forged currency and forged securities
3. Press items, roll films, photographs, phonograph disc, video disc, tape, video tape, laser video disc, laser audio disc and other items that are harmful to the country's politics, economy, culture, and social morals.
4. various deadly poisons
5. addictive substances, including, opium, morphine, heroin as well as other narcotics and psychotropic drugs.
6. Priceless relics and other museum pieces whose exportis prohibited.
7. Endangered plants and their specimens, seeds, as well as the materials for reproduction
8. Manuscript, roll film, photographs and other items related with the Offical Secrets of the country.