People assume a month needs more luggage than a week. It needs less — a week’s clothes and the willingness to wash them somewhere with a view.
The rules of the bag
Everything matches everything, everything rolls, and nothing comes along on a maybe. The bag must close with one hand and go under any train seat in Europe.
What the list buys you is not minimalism, it is mobility: the freedom to change towns on a whim because leaving takes four minutes. That freedom is worth more than a third pair of shoes.