What a wonderful cruise you are going to have. I am excited for you. I suggest you check out RCI's website for info. on all the excursions they offer. Also use the internet to do the same re. sightseeing. Dubrovnik is a wonderful "walking" city, by the way, and Venice is one of my favorite places in the whole world.
Have fun...and post here when you return, please, and tell us all about it.