What is the ruling on taking money allocated for breakfast and using it to buy other things besides breakfast, knowing that the shop owner has authorized the questioner in almost everything?

The shop owner's statement: "Take money from the shop and buy breakfast" is a permission for usufruct, not ownership. The difference between them is that ownership implies the right to dispose of the item, while permission removes the restriction from using something that is not owned. Accordingly, the questioner is not allowed to take the money and buy something other than breakfast food with it, because the one who is granted permission does not have the right to dispose of it in a manner other than that for which permission was granted. If she wishes to dispose of it otherwise, she must inform the shop owner and act based on his permission.