You’re right, it just doesn’t make sense to resort to cannibalism when you’ve got such a tiny population and there are all sorts of squirrels, possums, raccoons, snakes, fish, and big game available. I suspect the cannibalism is being done out of ideological reasons rather than practical ones.
As for the canned food, well, we don’t really know how long it took for the zombies to win. We don’t know how long Rick was in the hospital, but, since dehydration doesn’t take long to kill someone, we can suppose that he wasn’t without care for very long before waking up. And though we’re never really told how long it took for civilization to come to a screeching halt we do have some flashbacks from Shane and Laurie and later Michonne suggesting that it did take some time. There was time to establish refugee, er, evacuee camps and from Michonne’s flashback it looks like she may have been at one for a week or two before it was overrun.
An accurate timeline is difficult to establish but let’s say three weeks pass from the time Rick is shot until Atlanta is being bombed by the US Air Force (as seen in a season 2 flashback). And that the night Atlanta was bombed was the same day Rick’s hospital was overrun and Shane’s attempt at rescue failed.
[li]Rick is shot. [/li][li]The next day the news reports of violent riots in New York, Dallas, Los Angeles and in faraway places like Cairo, Munich, and Kiev. A significant minority of Americans rush to the market for food, fuel, and supplies. [/li][li]Three days later, thanks to the abundance of camera phones, the threat is clearly understood. New York, Dallas, and Los Angeles are being evacuated with the rising dead being reported in Seattle, Little Rock, Miami, and Denver. Americans as a whole make a mad dash to the market for food, supplies, and fuel. [/li][li]A week later normal economic activity has come to a halt. Martial law has been declared and food and essential supplies are being delivered to evacuee camps or other designated areas. Given the scope of the problem, distribution of food and supplies to those in need is difficult.[/li][li]Two weeks and the most of the larger cities belong to the dead now. Those who didn’t make it to an evacuee camp are running low on food and potable water. [/li][li]Three weeks pass and the walkers have overrun most of the evacuee camps. Shane’s attempt to rescue Rick from the hospital as soldiers euthanize the patients fails. The government’s attempt to hold Atlanta finally comes to an end as the US Air Force bombs the city to cover for their retreating forces.[/li][li]Rick wakes up the day after Atlanta is bombed.[/li][/ul]
And that’s the real reason why people still watch this show, my friends. It’s because it’s so fun to talk about, nit pick, and come up with fan theories. Oh, if such a short time passed why did Laurie fuck Shane? Well, their marriage was kind of on the rocks any way. I guess.