So I realize this isn’t anywhere near the focus right now, but I was thinking of it as a mode that could be done in the future. What is the single worst place you could be during the middle of a zombie apocalypse. Probably in the middle of a large, sprawling city, like New York or maybe Dallas. So in essence you would spawn in a single heavily barricaded building in the city… with no food what so ever. 
In a large city like this I would think looting would use up/move most of the food and other important resources away from the stores, though some may be left virtually untouched. Guns are generally considered illegal in New York while they are more common in Dallas. A option for difficulty?
We can already simulate most of this the current options, but I think we would lose access to some resources and tiles that only spawn in the wilderness. Like Labs and military bases and such. This has already been discussed somewhat in other threads but I thought I’d mention it as a mode/challenge of it’s own.
New Tile suggestions:
Disguised Lab: (looks like some other kind of tile but is really a front for a lab) houses an elevator leading to an underground lab (below the sewer system?).
Park: A small amount of wilderness in a larger city. These should very in size widely. 1x1, 2x2, 3x3 at the very least. 
Mall: This should be a gathering of random shops all crushed together in one massive building. At the very least 5x5 of just building and that surrounded by parking lots.