vade mecum | vay-dee-MEE-kum | noun
1 : a book for ready reference : manual
2 : something regularly carried about by a person

Example sentence:
Her latest book is an accessible and amusing vade mecum of the English literary tradition.

"Well into the 20th century, John Barlow's Ideal Handbook, the vade mecum of the rifleman, carried instructions for molding the Keene bullet." -- From Dan Shideler's book Gun Digest 2012

Learn more about vade mecum at Merriam-Webster Online.