American Practical Navigator by Nathaniel Bowditch
What to bring, then? A ship can be a small thing with little room for human bodies much less spare equipment. Of course, as the advice above notes, it is better to have a thing sitting around than to not have that same thing when your life depends on it. According to Peter H. Spectre, Bowditch recommended this bare minimum in the early 19th century:
A watch with a second hand for timing courses
Gimbaled lamp to light your charts
Barometer for forecasting weather
Parallel rulers for making courses
Dividers for stepping off distances
Pencils, paper, etc.
All of these things would most often have been found at the so called "navigation station" aboard ship. Generally, but not always, this would have been located in the captain's cabin. Today, much of the busy work has been eliminated by GPS and computers. All the same, better have the above just in case. Technology is a wonderful thing... until it ceases to function, that is.
Header: View of Ships Near Venice by Oliver D. Grover via American Gallery