Freshly provided. You have no idea if that container of milk sat out on a counter for 5 hours before being put back into the fridge. Same with the bread. Perhaps a kid fingered it before the parents got exasperated and shoved it back into the bag.
However, you don't have to provide a fresh bag of bread. You can get attractive containers or bags, and place an appropriate amount of bread out for the guest. Milk? buy a gallon and have attractive pitchers or bottles that are washed between guests to divide.
Butter is another one. Who doesn't know that you shouldn't dip your knife in the butter, use it on your bread, perhaps even lick the knife or stick it into jam, before putting that same knife into the butter once again? But, I have seen all of this.
I think your sister's guests probably do mind, but are too polite to say anything.
EDITED: to clean up typos