polaroid guest book. guests take a picture of themselves or get someone at the front table to, then they can write advice or well wishes on the back! and there can be a string and clothes pins and it adds decoration as the guests come in.
I know the grandparents and your family is really important to you too... something like this would be really pretty to have there. I like old photos and I know you are a history buff. This could incorporate a little of your two passions.