The best policy is to take as little as you can,and restrict it to what cannot be cheaply and easily obtained in China itself
Clothes: light ,loose,natural fibre,hand-washable clothes are best,plus one heavy jumper and a light waterproof jacket with a hood.Take stout walking shoes or boots with good support ,and a pair of flip-flops for use in hotel bedrooms and showers.
Many popular brands are now available throughout China,particularly the big cities.Good toothpaste is a little harder to find than familiar brands of soap or shampoo.Bring plenty of good sunblock and small quantities of whatever upmarket moisturiser or other cosmetics you can’t live without,as while these can be found in Beijing they usually cost more than they do at home.
Wearers of soft contact lenses will find solutions on sale on everywhere,but for hard lenses there’s only one source of supply in Beijing,the eye clinic
A Swiss army knife or other multi-purpose tool,and unbreakble mug for drinking hot water and making tea on Chiense trains
A North American to European adaptor or vice versa(just in case)
Photocopy the information pages of your passport and those holding the visas for your trip