Your admission ticket (准考证) and national ID card (身份证). Both checked, both in a transparent folder.
Two 2B pencils, already sharpened, plus a sharpener that catches the shavings and a soft eraser.
Two black-ink ballpoint pens. Not blue. Not gel, unless your province explicitly allows it.
For the maths and physics sessions: a transparent ruler, a pair of compasses and a set square.
A water bottle with the label peeled off. Some exam centres do not allow any labelled containers.
A packet of tissues and a small hand towel. Exam rooms in June can be warm.
Nothing electronic. No watch that vibrates, no smart band, no wireless earbuds in a pocket — not even switched off.
Pack the bag the night before and check it once in the morning. Do not repack it in the morning; that is exactly when things get left behind.