Here's an old trend that is making a reappearance. The trend is wax lined cake bags for guests to take leftover cake home at the end of the night. We did this recently at a wedding and it was a big hit. I really like the idea because there is almost always cake left over after the wedding that someone has to pack up and take home. When part of a layer is left it's hard to find someone that wants to take home that much cake, but slice it up, bag it and place it by the doors as your guest leave and they will love being able to carry a slice or two home.
Just have your caterer slice the left over cake and place it in your bags. The bags can come already decorated with wedding bells, etc., or you can have them specially printed with your monogram. What a nice way for your guests to remember your wedding.