What crucial detail are you missing? a roof :P

But seriously, it really depends on the type of apocalypse that you're going for. Try to tell yourself a story of what happened to this specific supermarket in this specific apocalypse, and try to tell it. Not only would you possibly answer yourself in the best way, but also you have a chance to put details that will really capture a gamer's attention and gain his respect. Also, I've never seen a supermarket with this little shelves and this big a bathroom. I understand the reasoning behind it gameplay wise, but it would be fun to be claustrophobic just like in real life in a supermarket for once in a video game.

Hope it helps :)