The four of them spend the day in Diagon Alley buying up his school supplies. Sirius insists on buying him a Nimbus, even though first-years aren’t technically allowed to bring brooms. Remus selects a number of books Harry simply must have, to complement his school textbooks; he’s still wary of spending too much, but since being hired at Gringotts, he’s been able to afford himself a few luxuries he simply couldn’t before (among those luxuries is apparently a nearly pathological need to buy Harry books because a man can never read too much, which is fair enough, Harry supposes).