No communication with family, no meeting. You can mail him underwear, socks, autumn and winter clothes, but you can't have letters, notes, clotheslines, shoelaces, metal zippers, ornaments, etc.
You can pay him to buy underwear, socks, toothbrushes and towels at the detention center; Snacks and other expenses, but the types and sizes of items in the detention center are limited, and each person is limited to a certain amount per month.
Generally, 200-300 yuan will do.