It's the setting of my game, Kid's Last Tour.
Humanity has fought its last war. People are thin on the ground, but you do find some. Some like Grandpa. He took care of you and your friends. He kept the machines running, made sure everyone had at least one meal a day. That everyone had a warm place to sleep.
But then he died.
It wasn't a surprise, he was old. And he made sure that you knew what to do when that day came. So you buried him in a pile of rubble, loaded up your vehicle and off you went into the ruins of the city...
I've run it several times and I really like how the players invariably go looking for someplace that they can set up a colony. So yeah, it's my submission for this prompt!