Date Night Jar
general journal junk
-
idealog
While this isn't a jar done in quite the way the others are, it's still a potentially unique gift. This is something I did for some friends when they married - though I did it in a box to match the wedding colours. For the first, I did this at the engagement party, and the other at the wedding reception.
Have a receptacle of appropriate choice set somewhere it's easy to access, and have guests at whatever event you're attending write ideas for date nights on the card for the couple and put them in the receptacle. You can also put some cards and pens at each table so it's easier for guests to take part, as well as cards and pens at the box location. The couple can draw from it whenever they like and do what's written on the card as a way to reminisce about their wedding and to enjoy each other's company.