There is only one EOTWAWKI book - Black Easter by James Blish.
The premise of the book is that ritual magic and demonology as described in grimoires such as the Key of Solomon actually works.
An arms manufacturer who has gotten bored with fomenting conflicts so that he can sell weapons to both sides seeks out the worlds foremost black magician, so he can loose all the demons in Hell onto the earth for a day, just to see what happens....
I won't be spoiling the plot by mentioning it doesn't quite work out as planned
All my life I been in the dog house
I guess that just where I belong
That just the way the dice roll
Do my dog house song
For post-apolalyptic fun, I suggest the Horseclans books. Keep you busy for a while.
Maybe we're just jaded, but your villainy is not particularly impressive. -Ennesby
If you know what you're doing, you're not learning anything. -Unknown
Sanity is the process by which you continually adjust your beliefs so they are predictively sound. -esr