One thing I am playing with adding to our guest book table at our AHR, which could totally work in your passport, is a page each for "Things You May Not Know About Him/Her", with little tidbits about each of you, or "About Us"... since not all your guests would know little details. I incorporated that into a puzzle in our welcome books... things like, the first movie we watched together. Some easier stuff too, like name our pets. I am not sure how much that would fit for you though.
I am a teacher, so I put an information packet together about the country and region. You could do something on a smaller scale on a page. Or trivia.
In my classroom I have a daily "Did You Know?"... So I put a Wedding-themed "Did You Know" together as part of our one-month mail-out too. Things like, where certain traditions come from. Like why we wear wedding bands on our 4th finger left hand. Or the percentage of men who propose on bended knee.
Or wedding traditions around the world. This could be very cool if you include your family histories in them too.
You could add a couple engagement pictures, if you did those.
Did you want to include any note about photographs? I am not, but I have seen brides request, on a page, that wedding details be kept off facebook and other social media sites. Or to share pictures after the big day on shutterfly or whatever.
Or how about an RSVP page?
Hopefully some of those ideas helped! Good luck!