First of all, the most important necessities for touring Tibet are your certificates and travel documents. Please keep them with you safely at all times.
Heavy clothes – The weather temperature varies violently in the morning and evening. Even in June or July it is better to bring with you enough heavy clothes such as woolen sweater and down coat. A windbreaker plus a sweater will work nicely for strolling around Lhasa in summer. A down coat is necessary for those who are traveling beyond Lhasa and Shigatse into more remote areas such as the Everest Camp. Wearing several layers of clothing that can be easily added or removed will be a smart choice.
Tibet has strong ultraviolet ray. In addition to sunglasses, it is useful to bring some lip balms and sun blocks to prevent sunburn. A wide brimmed hat can be very practical there.
Most annual rainfall comes in the rainy season that starts from June to September. Frequent rainfall makes waterproof clothing and raingear absolute necessities. In addition, you should be ready to meet landslide and car broken in your tours in Tibet.
Sufficient amount of money since ATMs are few in the more remote areas.
Solid food and drinks – You should bring enough high-calorie solid food with you, such as cookie, chocolate, and candy. Also you should bring enough drinking water.
All necessary toilet items including small packages of tissues and either a battery operated shaver or razor
Many places in Tibet that deserves your visit have poor lighting. A nice flash light will be of great use.
Sleeping bag – It is necessary for those who enter Tibet through land or tour other places than Lhasa.
Louse-killing powder – Except Lhasa, most places in Tibet have simple hotels. Maybe there are lice around. It is better to spread some louse-killing powder.
A first aid kit including aspirin, antibiotics and AMS medication is highly recommended.