Get the Vaporetta pass and enjoy this unique and beautiful port. Also, if you are doing an overnight on the ship there is a people mover about two blocks from the dock that will take you into Venice in less than five minutes for l Euro. When you get off the People Mover you will be in Piazzale Roma with access to Vaporettas and connecting bridges to the rest of Venice. If you need any supplies or beverages ask directions to the Coop which is close to the station. This is a Venetian Version of a discount store and you can purchase supplies and beverages at a much better price than other places in Venice (especially wine and soft drinks.)
We stopped twice on different legs of the cruise. Each time I enjoyed the beauty more than before. Take a ride in the cable cars or if you are adventurous ride up on the donkeys. Either way you will arrive at a beautiful city full of neat shops and restaurants.
Walk from the port to Columbus Square and then amble up the Ramblas. There is a wide esplanade down the middle that is filled with shops and street performers. To see a lot of Barcelona for an economical price I suggest the Hop-on, Hop-off buses. If you ride the buses get off at the stop where the beautiful Gaudi Church La Sagrada Familia is located. It contains some of the most beautiful stained glass windows I have ever seen.