You should realize that you will spend 2 nights in the train. The Qinghai-Tibet Train is considered as a 3-star facility train in China, but it is not a hotel, no disposable provided. You need to prepare your own slippers, towel, cup, teeth brush, teeth paste, soap, even tissue paper to the train. Another problem you have to think about is the food, although there is a restaurant car in the middle of the train which provides Chinese food. At least you need think about to buy some milk, bread, fruit, etc. for the train journey. Tibet train has heating and cooling, so you do not need to ware too much in the train.