...turning on and off music isn't great for flow.
Meg's right: put the music on that fits the GAME
writ large and don't fiddle with it for themes or scenes or characters or whatever unless your session tends to have set downtime right before major scene shifts (never my experience, particularly with AW). Either that, or you better be a damn good DJ as well as an MC, seamlessly cutting in the appropriate music at the appropriate times.
All that being said, I have a few favorite
general background albums that convey an "apocalyptic" feel. Since I'm an electronica junkie and not into all this "rock" that others appear to enjoy, well, that's just reflected in my album selection. YMMV.
ARTIST - ALBUM
1. Evan Bartholomew – Secret Entries into Darkness
I classify it as "dark ambient." It was my background soundtrack while I ran
The Journey (
http://jeepen.org/games/thejourney/) at Fastaval 2010, and did the job. Think of it as a soundtrack for the cold wastes.
2. The Sight Below - Glider
Lots of white noise mixed with wafty guitars and beats.
3. The Suicide of Western Culture (self-titled)
Put it on softly in the background, and random anthems will match up to your characters' actions.