I don't carry a specific EDC traditional ink based pen, however I do have a thin point Sharpie that IMO, is much more versatile then any ink pen and can be used to write on almost any type of object/material out there.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock