Several of the "Where there is no ..." series of health books by the Hesperian Foundation are free for download in PDF-format.
Where There Is No Doctor.
Where There Is No Dentist.
Where Women Have No Doctor.
A Book for Midwives.
A Community Guide to Environmental Health.
... and many others.
Perhaps more meant for people, groups and organisations in countries with limited access to health care. But given TEOTWAWKI that may be us...
http://hesperian.org/books-and-resources/
Also as hard copy. For instance:
The Preparedness Set, Paperback, $59:
Where There Is No Doctor + Where There Is No Dentist + Where There Is No Animal Doctor,
https://store.hesperian.org/prod/Preparedness_Set.html