I like the way they did it in Left 4 Dead -- all ammo and items were left by other survivors, for any survivors that might come through after them (such as yourself). It helped give the sense that while your group was alone in a very real sense, that you aren't a part of a group of 4 people that are somehow the last remaining humans on Earth.
That way, if you actually manage to escape and get rescued, then you can co-mingle with all of the other dozens/hundreds/thousands of other survivors, and help rebuild society.
That way, if you actually manage to escape and get rescued, then you can co-mingle with all of the other dozens/hundreds/thousands of other survivors, and help rebuild society.