So basically everything is dead and the last thing to eat is humans? Was it a nuclear explosion (if it was, then even the cannibals are screwed)? I haven't seen movie/read the book, but i know enough about what happens to get a decent idea of how it plays out. What happens when the human livestock run out?
I wonder if this could be a good possibility if something like Yellowstone blows?
Even in a dead world, humans could survive. Nuclear power and a big underground greenhouse structure could allow you to grow food...although it wouldn't amount to much... I know of an underground corn growing setup that kicked out 3 crops a year

Anyone that needs recent history on cannibalism, take a look at the Japanese during WWII. I think somewhere in the Pacific the troops started eating the prisoners (Japanese soldiers were never supplied with much food). I think even an American or two were on the menu...
Edit: So after a little research it looks like the cannibals aren't too worried about long term survival. It may have made better sense to kill the humans right away, because by starving them, each day they are losing nutrition value. Its a losing battle if nature around you is dead. With no new inputs. Chop them up and freeze them. I wonder if a wind generator would still work, or is the wind gone too?
lawns should be outlawed.