Message in a bottle for anniversaries. Have wedding Guests write a note(s) and they can choose what year to personalize their note for. Then they stick it in the appropriate bottle! Married couple reads the notes on the matching anniversaries.
Save the Date - was thinking about the thumb prints for the wedding invite but this is a gorgeous idea to carry through from save the date to the wedding. This could be really cute to do on the wedding day to frame and for inside of the thank you cards?