So, a single man can kill as many zombies he want and eat food from the ground and the army, with better supplies and weapons can't just kill some invisible super zombies?
There should be a menu with the survivors' body design. Then, you could equip all the gear. This would get the survivors like super soldiers, so the gear should have lower effect.
There should be a way (a book, or something else) of chaining through buildings of the same area, like a warehouse and a street, or an office and a police station.+ if you agree.
If you save and load, the dead NPCs get back to life