What to pack for Tibet trip?

It is suggested to pack more stuff when travel to Tibet.
Backpacks: one large backpack and a small one. Large one for remote trek and small one for daily city trip.
Clothing: pack more layers, warm sweaters, cold proof clothes, wind-proof shoes, water-proof clothing, hiking boots, woolen socks and warm gloves.
Food: it is suggested to pack some drink water and snacks
Medicine: pain-killers, medicines for colds and fever, some purification tablets for your drinking water, and also oxygen bag etc
Protection against sunburn: it is necessary to pack your sunglasses, sunhat and suntan lotion or sun-cream.
Lighting: pack torches and candles in case of power cut.
Important Documents and contact numbers