your running-out-of-gas fire truck

The radiator is behind the cab, where the engine is. See? no grille.

were well-done, including the camera tilts that made sure the whole sequence looked creepy and dangerous

So, it pretty much has to be presumed that the government, military, etc. are either destroyed or greatly diminished and in hiding.

Rational thought is not your friend when it comes to TWD.

Any postapocalyptic scenario is by and large impossible anyway, considering the nuclear plants would soon melt down after a collapse like that, and the ensuing fallout would swiftly kill everyone and make the planet uninhabitable that I've watched "Aftermath".