Keep certain things out of the market buildings.

[estherhb]

The categories (flags) of items stored in a market are part of the code and can't be made so they can be selected by the gamer.  You can create custom marketplaces by using the edibles market plus the smaller market carts and market stalls.  Each one stores one of the carts and stalls stores one specific flag.  The downside is that each one uses one vendor, while a Central Market can be staffed with just one vendor (or more if you prefer).    The Wiki contains more info regarding market carts and market stalls.

[Elvenkind]

Charcoal no. Fuel in a market a bad idea? No.


Stone and Wood. Yes, I'd say that's for piling up outside somewhere, or in mentioned facilities made for it. When those are full to pile up next to them.