Fuck 4x4's. Fuck Hummers.
The Dead Reckoning is where it's at:
I love using that picture. : D
A few more ideas that may-or-may not be usable:
-Larger central buildings, almost designed to be strongholds. In this case, the police station, local high school, or weather shelter you can use for yourself.
-Automated turrets, if they're not already in. Would obviously require a ton of experience with electronics, mechanics, and guns.
-Bicycles and horses, once you add in vehicles. Bicycles would not contribute to your overall carrying capacity, but you should be able to store some stuff on a tamed animal.
-Expanding from that, the ability to tame animals! (Like the dog that you start with). Each animal or creature would be required to be tamed in different ways, and you could even make a skill to track that. Perhaps, with a certain trait or high enough skill in taming, you could train zombies? (With a chain and a couple of pounds of rotten meat, of course. They probably wouldn't follow you around like a dog, though.)
-Banks; another idea for a possible 'stronghold' building.
-I thought it'd be cool to be able to choose your ex-profession, which determined certain skill bonuses and some starting items. For instance; an ex-mechanic might start with a few tools and a mediocre mechanical experience. A ex-police officer might start with a handgun with a bit of ammo, and firearms experience.
-The ability to build barricades outside of windows and doors. Simple enough, it'd require 5-6 two by fours and some rope, along with a few nails.
-Furniture inside the house besides wardrobes and refrigerators. Would only really serve as a visual addition to the game, until later when you can smash them up for more building material.
-Roving bands of powerful infected that appear on the map as a 'H' or something similar (for horde). If you choose to be a nomad-type character, they wouldn't be much of a threat unless you were careless enough to wander into them. If they decide to come near your stronghold, though, you'd have to hold out or abandon it.
-Swords! Maybe a really rare 'DnD Shop' or something like that would have them.
-Metal working skills, melting down certain tools to make other tools, or custom items you need for certain crazy contraptions. Would require a buildable forge and coal. (Just suggesting this because of the whole Bay12 thing.)
-And finally, large department stores infested with zombies on the map, themed around a certain type of store. (Sweetbay for groceries, Home-Depot for hardware, Walmart for general-type stores.) They'd be filled to the brim with items you otherwise couldn't get, but at a cost: They'd be filled with all matter of zombies, and you'd need a flashlight with a decent weapon to take them over.
If you ever decide to open up the blog again, you'd definitely have an avid reader-base. You'd probably attract more people to the game, as well. (I'm not sure if that's a good or bad thing at this stage of development.)