I need a word that defines that which is commonly tossed aside to be grabbed back again, like a notebook. I'm trying to use a word that defines this implicit nature in an object: something that is not that important, but at the same time is when you need to jot something down.
Once a _____ notebook on which employers, directors, engineers, and visitors jotted down interesting events of the achievements of that time, has become the sacred book of The Company.