Both yes and no. The store is part of a chain, and orders it's supply from them, who send out trucks from central warehouses (some exceptions may apply, like local eggs/milk or produce/fruit, or frozen goods), with only what is needed at that time. They know when and how much they usually need (typical weekly, or annually for holidays and such), and what they will have room for. Due to order volumes of the chain and purchasing power at that volume, including attached contracts, this usually works out. If not, some shelves might be empty, it happens.

Keep in mind that the warehouse aren't days away, and do have supply. How quickly they can get stuff in depends, but might be "tomorrow" if needed. Also friends if a delivery is already scheduled and/or if it has room and so on.