ROOMs as minimal units of prep
1.
Think of the room as the minimal unit of prep. Faced with a blank page, just make a room. (Dungeon23's Sean McCoy showed that making a room a day is a worthy creative exercise).
2.
A room doesn't have to be a room.
The class is abstract, and we can determine its scale. It is possible to treat a journey of several days as a room. It doesn't even have to be a physical space.
3.
Some might prefer the word scene, but I find that is inevitably linked to plot.