Mad Libs: Leave a printout at each guest's place setting instructing guests to write personalized vows for the newlyweds. Read a few of the funniest responses out loud before or after opening the gifts.
It's not super rustic and I don't know about the bow/flower thingy... But the idea for a card holder is good. You could use a galvanized bucket with a chalkboard or something. I think I pinned something like that for you.