Along the same line as the bases suggestions, and with suggestions of adding dangerous wildlife to the wilderness as well as enhanced vehicle damage/repair there are a few things I'd like to see. Buildings in towns currently only serve as spawn points for various loots, you wouldn't want to stay in them for long. If you could close the doors (assuming you entered with no aggro) and then have that building be for the most part safe they could easily become urban camps. Currently people barricade buildings with sandbags and razor wire anyway, maybe an included storage system and improved line of sight/zombie collision would be enticing. This would be especially interesting if an unprotected camp in the woods could attract unfriendly creatures, such as the suggested bears and wolves. Along with this two new items to the vehicle repair system could be interesting, keys and something for hot wiring such as just a wire, or perhaps a tool kit of some sort would make more sense. The system could be implemented so you could find a key and it goes in your tool belt, then if your the first person to a car your key is the only one that works. It could be transferable so if you were killed it could be looted or you could trade it. On the flip side if you had a tool kit you could hot wire an already accessed car or a car that still needs a key and take it but it would take a few moments to start every time. Both of these items could be added to the possible loot just like repair parts.