Dean King's Sea of Words and Harbors and High Seas are pretty essential, I find.
I also like Patrick O'Brian's Navy: An Illustrated Guide to Jack Aubrey's World, though it's more 'additional reading' than a must-have, for me.
And of course, Lobscouse and Spotted Dog is the essential culinary companion, if you've a mind to spend some time in the galley and want to shout "Which it'll be ready when it's ready!" as authentically as possible.
I've heard good things about the Patrick O'Brian Muster Book, but I haven't used it so I can't speak to it personally.
Do you know about A Sea of Words by Dean King? It’s a lexicon/companion to the series and helps with the nautical terms. There’s a German edition: https://www.amazon.de/-/en/Dean-King-ebook/dp/B007DFUQ72