A guestbook is a fun way to remember all the guests who were adventurous enough to make this journey with you.  While you can find cool, Costa Rican themed journals and the like in the souvenir shops, again I’d recommend bringing your guestbook with you. Even if you find a book here that you’d rather use, you can always set aside the book you brought. However, if you don’t find one here and don’t bring one with you, you’re out of luck. A good-quality pen, perhaps with fancy decoration is nice to include with your guestbook.