Cake

Ok. So here's what I think would be the simplest and most elegant. Especially since you two are going with a black dress and a white dress (which is very chic)

Buttercream frosted chocolate cake, black satin ribbon

White frosting, black satin ribbon.

But yours will be 3 tiers:

and we can add flowers (imagine that these are blue, not white):

 

Considering that this is just a white cake, too, and not something too crazy, we could probably do a fondant (like the center picture) that we could easily make out of marshmallows.