hi zhejiang rider.
The only stuff you must carry is 行驶证 and driver license, and according to the law, you should also carry your insurance card(can be put into 行驶证) and the sign of 检验(a little piece of paper can be put into 行驶证 too)

If you don't do the 检验, when you are checked by the police, the bike will be taken by them, and you pay the fine for that. After that if you don't 检验 for more than 3 times, you bike will be scraped if you are catch by the police.