This post is a bit of a cheat since I am going to suggest some things technically included in the Venice UNESCO World Heritage inscription. However, these three things are to fill up your itinerary once you are already in Venice. While some are obvious, others you might not have considered.
1) Stroll Around at Night Time
The first thing you will notice in Italy is The Grand Canal. What is the second thing you ask? The CROWDS! I didn’t try to look very hard, but I didn’t notice much of a “night scene” in Venice besides a few scattered restaurants that were open. Furthermore, from my personal observation, the majority of the crowds came from cruise ships and were much older than me (20’s). Maybe it was a combination of these three things that makes Venice quiet at night, which is a good thing! The canals, and the city in general is as aesthetically pleasing at night as it is in the day.