Pack breathable layers for most of China, add warm insulation for northern winter, and include rain protection and quick-dry items for the hot, humid, rainy season in the south.
Clothing
Lightweight tops (breathable fabrics for humid summers)
Long-sleeve shirt or blouse (sun protection and air-conditioned interiors)
Pants/jeans (modest, versatile for cities and temples)
One nicer outfit (for upscale restaurants or business settings)
Comfortable layers (spring/autumn and chilly indoor AC)
Warm coat or insulated jacket (winter in northern China)
Socks and underwear (extra pairs for long transit days)
Sleepwear (lightweight, easy to wash)
Scarf or shawl (useful for sun, cool evenings, and modesty)
Footwear
Comfortable walking shoes (for lots of city walking)
Slip-on shoes (easy for airports, trains, and security checks)
Waterproof shoes or sneakers (rainy season and wet sidewalks)
Sandals or breathable shoes (summer heat and humidity)
Dress shoes or flats (if attending formal events)
Extra insoles/blister patches (long sightseeing days)
Toiletries & Health
Sunscreen (high SPF; UV can be strong in many regions)
Insect repellent (especially in southern and rural areas)
Personal medications (bring enough for the full trip)
Motion sickness tablets (helpful on winding roads or trains)