Have passport, will travel.
Have suitcase, will travel.
In both examples, it means "I have a .... and am willing to travel". Obviously, both a passport and a suitcase would be quite helpful when travelling!
I can only assume that the speaker of your phrase is perhaps a travel writer, so it would be very useful for him to have a pen (quill pens being the old pens made of a feather dipped in ink to write). It's my best guess.
If you could give us more context, that would be good.