Right now in 2011, a lot of cities in the US and to a lesser degree Canada have some pretty large abandoned spaces. It is not remarkably difficult for groups to take over abandoned space and put it to use, although in an economic collapse scenario, that means maintaining convoy mobility to the point you can rally up and roll out if the heat is on. I know of a few huge empty warehouse type places here in the Portland area that could fairly quickly be converted to indoor RV parks with power, water, and even natural gas hookups with only minimal work, although toilets would have to run through existing building plumbing which could easily handle it. It would be a simple matter of retrofitting some of the larger restrooms with showers, fixing gate and security systems, and you are in. This is in consideration that one humbling factor for survival in the long term is when the weather turns cold and bad. To put that simply, it is easier to heat buildings than tents.
As for protein running around, I have literally seen more deer in one of the industrial areas of Portland than on my average trip out to the nearby mountains. The deer I stalked hang out in some abandoned and semi-abandoned industrial areas and feed on what I think used to be decorative gardens with berries and some fairly healthy plantlife considering the toxic crap that is probbly around there.
Another thing about cities is just like their original intent, they are transport, shipping and trade hubs, which means supplies get stored in cities, not out in the boonies. Fuel, medical supplies, manufactured goods, that is all what you find in the cities. Nobody makes fuel out in the boonies, it is made in refineries on the edges of cities. Breweries and distilleries can be re-purposed to make ethanol or even methanol fuel, and around cities, you can usually find an employable pool of expertise in technical matters that you don't regulary find in the country.
For example, right now I am going through some changes in my personal motor pool, and living in a major metro area have found it much cheaper and easier to find cost effective experts in getting my rolling stock up to par. Even comparing who can be hired or where to find work on Craigslist in major cities vs country areas tells a lot of the story.
I think whether you are in a pre-shtf situation or post-shtf situation, a lot of your financial success when getting your "life in the boonies" act together is well handled by people who can navigate city life, and then facilitate or do their trade between city and country.
That said, about the ONLY commodity that the city needs from the country is food, not really a whole lot else, except in circumstances where in a pre-SHTF city situation storage costs are so high in the city that you need the country people and space for extra vehicles and supplies that are not cost effective to keep in the city. Then there is also the situation of weapons caches. I personally don't think an apartment dweller in the city should have much more than the basic loadout anyway, partly because apartments are so unsecure.
I personally like living in the city, the more urban the better, and I like being out in the boonies. It is that in-between type of land, the McMansion and strip mall landscape that really turns me off. I personally think it is one of the harder areas to survive in too since resources tend to not be within walking distance.
Whether you are in the city or country, survival surrounds your vehicle. In the country it is usually going to mean your 4X4 truck. Suburbia you can get away with the SUV or minivan.
In the city though, you have vehicle security issues, so open bed pickups are pretty much out of the question. You can get some use out of camper shells and tonneau covers, but nothing really beats the regular full size van for cost effective practicality. OK, in some cases, smaller vans are good too.
A word on small vans, the real heyday of small practical vans came and went in the 1980s, so whatever you find in the small van market that is survivor friendly is going to be "vintage". That is the old Toyota vans, the ultra rare Mitsubishis, and of course the Volkswagons with their cult following. Vans give you the best combination of lockable cargo space, fuel economy, lower purchase cost and horsepower to weight rations than any other type of vehicle. The other space efficiency issue is with parking. Vans tend to give more space in the vehicle when compared to the length of the vehicle thus better turn radius and the ability to utilize smaller parking spaces. They also give you the better options for hauling trade cargo out to the country areas but you have the limitation of the vans being road use vehicles, not particularly suitable for serious four wheeling, even when you can obtain AWD or true 4X4 variants.
Another thing to consider about the city is relatively easy access to facilities, IE laundry, bathrooms, food. I know here, I can find big box grocery stores with sale prices a hell of a lot cheaper than the small town groceries that are the last stop before heading to the mountains.
