If we wanted to "go there," there are a lot of things that are basically too good to be true. With a limited food supply, it appears many of the characters gained weight instead of losing any. They also seem to usually appear pretty clean and well dressed . . . their clothes look to be in decent shape, they normally have decent haircuts, etc. It seems like they scavenge for guns and sometimes food, but not a lot of clothing / footwear / outerwear, etc.
Medicine and dentistry would be coming into play by now as well. The food they scavenge for would likely be stale or past the point of being edible. Even if they came across a supermarket that hadn't been touched at all, realistically, how much of food that is 2+ years old would still be safe to eat?
Although there has been some debate over the following, it's questionable if the vehicles could still run well on the gasoline that's available (could be too old and sludgy). Also they would need general maintenance and repairs, which might be in short supply. I also find it odd that the vehicles they found that work are old and not in great shape to begin with. The abandoned cars are also all old. Did anyone drive recent makes and models?
I am also curious at what point would groups decide that it is too much effort to go out and collect things, ie too far away to go out and search and come back, before they decide it's time to move to a new location. Maybe there's more available locally than anticipated (as others have said, there are probably lots of shopping areas available locally), but they usually show them going house to house, not store to store. They could probably load up on apparel at a mall, but they just haven't shown anyone do that.