You cannot leave Florence without seeing the outside of the Duomo! I attached just one of the websites that you can reserve tickets for inside entry. These are the most basic tickets - I would suggest upgrading to a ticket that allows you to skip the line for entry.
Vivoli is the BEST place to go for an affogato, the bride and groom will be wanting to go every morning!! Brides favorite- Pistachio Grooms favorite- Original
There are wine windows all over the city of Florence, so keep your eye out!
A historic square with sculptures and the old town hall. Great places to eat in the square and feels like the central hub of Florence.
If you don't mind a slight uphill walk, you must go see Piazzale Michelangelo (available to get there by car if you do not want to walk). You will have the most amazing view of the whole city of Florence. Bar is available when you get to the top!
Go home with a cute souvineer of a photobooth strip! One of our favorite keepsakes from our travels. There should be many fotoautomatica's in the area and it only costs 2 euros.