Given that we accept that the zombie apocalypse happened in a manner similar to the way it happened in The Walking Dead; is the reality faced by the survivors realistically portrayed?
First, we know little about the beginning of the apocalypse (<PERSON> "wakes up" weeks after it started) so we don't know if there were enough survivors initially to deplete the non-perishable food supply. If people died quickly, there would be more non-perishables for survivors. If not, there would be less. But clearly there would be competition for what's left which would increase with time.
However, what the show doesn't portray (for dramatic tension, most likely) is the quite significant amount of food available to survivalists in nature. Also, it appears that animals were unaffected. The decrease of human competition for habitat should result in an increase of animals that can run faster than zombies.
Gasoline is unrealistically portrayed in the show. Gasoline goes bad over the course of a year (without specific additives to boost it) and you couldn't get good gasoline from stranded cars, etc. (For example, in a car's tank, about 2% of gasoline evaporates/week, with the more volatile components going first.) Without a refinery, there shouldn't be any more usable gasoline for cars and other machinery (it might still be good for other things - setting fires, maybe some explosives).
Tanks, RV's, etc. 934
are not fuel efficient.
Self defense against a large group of evil people takes a lot of people - a large group - of even more cunning people, and survivors would tend to have a greater percentage of cunning people. However, the show doesn't thrive on the successes of the good people; it thrives on tension created by the conflict and dangers they face.
Finally, there is very little realism in the portrayal of injuries and death. Take a stab wound to the abdomen, or a gut shot. As in many television shows, writers of TWD imply in their storytelling that blood loss is the major killer in abdominal wounds, when in fact, the major killer is peritonitis and sepsis from a nick of a part of the intestines. In TWD, if they can just stem the flow of blood, most injuries are survived. This is very unrealistic. Penetrating abdominal trauma has a high mortality rate; that's why almost every case of penetrating abdominal trauma goes to the OR. Chest wounds are similarly unrealistically portrayed.
So, no, the world of TWD is not very realistically portrayed. 238