Vade mecum is a noun that refers to something regularly carried by a person.

Coming directly from a Latin phrase that translates to ‘come with me,’ our word of the day, after entering English in the early 17th century, came to refer to anything typically carried by a person. It sometimes refers more specifically to a handbook to be constantly kept around. For example:

When travelling through Italy, I found an English to Italian dictionary invaluable. I always kept it nearby for those occasions where I didn’t want to eat food too spicy.