Charles Ellicott Commentary Genesis 41:48

"And he gathered up all the food of the seven years which were in the land of Egypt, and laid up the food in the cities: the food of the field, which was round about every city, laid he up in the same." — Genesis 41:48 (ASV)

All the food. —Probably, besides the fifth paid as tax to the king (and from which all the current expenses of the realm would have to be provided), Joseph bought corn extensively during these years when it was at its cheapest.