You can't buy your own food in prison, but it's all in one pot, provided by the state. In some prisons, you may arrange labor and learn some related skills, which is voluntary labor and no salary.
China's "Prison Law" stipulates that Article 50 The living standard of prisoners shall be calculated according to the physical quantity and set by the state.
At present, the national food standard for criminals is not lower than the per capita living standard of local prisons. The basic principles are: complete, cooked and hygienic. At present, there are basically no coarse grains. In order to stabilize prisoners' mood and arouse their enthusiasm for reform, the prison also provides living allowances, and often supplies meat, eggs and milk, which need to be improved on holidays. As for the specific diet, we should combine local customs, such as rice in the south and steamed bread and pasta in the north.