Karen - I've done the same thing. I have a box for all the wedding stuff. All my RSVP's are in there, receipts, etc. It'll be a great thing to keep and look back on in later years. My parents kept a book and it's really cool to see how much they paid for a hotel on their wedding night, which was $32, 34 years ago - so neat!!!
I'm a little scared of making time for writting while we're away, but I think I'll manage. FI will be pretty good at keeping up too, he likes that kind of thing!