In ancient times it was a Jewish custom recorded in the Mishnah, Talmud, and Midrash to carry a mezuzah in a walking stick for protection. It was used for personal spiritual fortification, and not solely to fulfill the halacha of being affixed to the doorways of buildings where Jews reside.
It is easily understood that a non-kosher mezuzah does not possess any protective qualities. Therefore, when, G-d forbid, someone is sick or there is some other misfortune, the very first move by an observant Jew (after calling 911) is to check the mezuzahs in the house. If some of the mezuzahs turn out to be posul, they get fixed or replaced. This has always been the Jewish custom.
The first Chabad Rebbe, Rabbi Schneur Zalman of Liadi, had a mezuzah near him at all times in fulfillment of the verse, “I have set G-d before me always.” (Psalms XVI, 8) Rebbetzin Chaya Moushka, the wife of Rabbi Menachem Mendel Schneerson, used to keep a mezuzah in the glove compartment of her car. The Rebbe himself kept a mezuzah on the desk during private audiences. There are many more instances of present- day personal mezuzah usage.
So, if you walk, sit, or drive, (not dive), or just generally hang out somewhere far off the beaten path, it may be time to consider having your own personal mezuzah to keep, just in case………..or in a case. I’m just sayin………………………