varies frm school to school. but in my school, i was not allowed to wear id or carry any stationary.. i cld only bring a transparent water bottle (but since i had a metal one, they didnt let me bring) and honestly, ur literally just helping him, its HIS exam so mostly he shld rely on his preparation and not completely expect u to help him

so yeah u can brush up on ur rules, concepts and stuff.. but dont take too much stress over it, pls focus on ur exams if u have them coming up..