I love this idea. An envelope guest book. You just take a store-bought scrapbook/album and glue envelopes into it. Lay out colored pieces of paper for guests to jot notes down on, and then they can place them in the envelopes.
Just when we thought sticky notes can’t get any better - they did! The Pocket Sticky Note does more than being handy for your notes, lists, and reminders. It has a real pocket for you to fill with you (Diy Paper Envelopes)