Every year travelers get stopped at customs for rules they didn't know. This list keeps your passage smooth.
Absolutely prohibited: all drugs and paraphernalia; firearms, ammunition and imitation weapons; controlled knives; ivory, rhino horn and other endangered-species products (even antique crafts); subversive or obscene publications.
Food restrictions: fresh fruit, vegetables, meat, eggs and dairy are banned (pest and disease risk) — mooncakes and zongzi with meat or egg filling often get stopped too. Sealed ordinary snacks, chocolate and tea are usually fine.
Medicines: carry prescriptions or doctor's notes (in English) for prescription drugs. Narcotic and psychotropic medicines (sleeping pills, codeine products) require customs declaration, medical documentation and sometimes a special permit.
Cash limits: up to $5,000 without declaration; above that (or equivalent foreign currency) you must declare. RMB cash is capped at ¥20,000.
Others: duty-free alcohol 1.5 L, cigarettes 400. Personal electronics (phone, laptop) are fine as normal personal effects.