Purchasing bags has been a thing here in Europe for years, sales have not dipped and people bring their own bags, carry the items or put them in their pockets, backpacks or whatever. Why do you need four bags? Either take bags from home so you are ready or buy one (or two if necessary) and just share them amongst you, you don’t need a bag each. Empty them out in your room and take the same bags back the next day. You will not end up with a house full if you do it properly, buy a few and constantly reuse them until they fall apart and then recycle them and replace them. It might take a while to get used to but it certainly isn’t difficult.