Day trip from Florence

Everyone has their favorite towns for a day trip near Florence. Unfortunately, most of the ones you can get to by public transportation are going to be more touristy, and the more tourists, the less charm.

I'd recommend Fiesole, because it's really close to Florence. In fact, you can get there by local bus service. You could even walk (it's about 1 1/2 to 2 hours walk.) It's up on a hill overlooking Florence (so if you want to walk, you might consider taking the bus up and walking back). Since you only have three nights, it'll be much quicker and easier than heading to one of the more visited hill towns like San Gimignano or Volterra.

We really liked Volterra--maybe 1/2 hour southwest of San Gimignano. It's quite a bit larger town than San Gimi., and is quite an impressive sight.

It sounds like you have been to the area before, otherwise would not plan a full day trip out if you only have 3 nights for Florence.
From my limited knowledge of bus transit options to the smaller towns is that it is more of a commuter schedule than a tourists schedule, so I suspect it could be done, but likely requires leaving early and not returning until end of day with no option of leaving early. You could look up schedules for Montepulciano which you might like and has great wine, it is also large enough that it could occupy your whole day, if the town is too small it may be charming but with no car after a few hours there you may be very bored. If you want to see a vineyard those are outside of the town walls but there are places in town that offer wine tasting.

Consider Pistoia, only a 25 minute train ride away from Florence-.

Nearby are Arezzo, Anghiari, and Sansepolcro, buses can get you there.

Arezzo is an easy train ride from Florence then you can take a bus to Anghiari or continue by train to Cortona. It's a lot for one day but doable. Arezzo is a wonderful old town, very easy walk from train station to the historic center. The famous and fabulous Legend of the True Cross frescoes are there, by Piero Della Francesca. You need a reserved time to see them. Pistoia is often recommended because it was designated for 2017 as the cultural capital of Italy - not sure of the exact designation but it is a big honor for the chosen city.

I echo Susan's Arezzo recommendation- it has a very helpful Tourist Office right beside the train station, several lovely churches, a medieval to modern art museum, and wonderful food. All of the sites are within easy walking distance of the train station and you could add in a bus trip to Sansepolcro but be sure to check opening times for the civic museum. (The Arezzo TI can provide a Sansepolcro map and help with travel logistics). Life Is Beautiful was filmed in Arezzo and there are small plaques identifying scene locations throughout the town. Transportation to Arezzo is easy and inexpensive from Florence by train.

Wow... thank you everyone for the great recommendations. I'm going to start researching these places. Yes, I've been to Florence twice before and been to all the museums, hiked the Duomo and explored the city. We are hoping to take one day trip from Florence and spend the other day in Florence. Thank you!

Not a small town, but Bologna has fantastic food and is only a 30 minute train ride from SMN.

Another vote for Fiesole. We were just in Florence two weeks ago and took the bus for 2 euros and went to the Christmas market in Fiesole. It's a short 20 minute ride from Florence and was a nice break from the city. We had an delicious lunch with incredible views at La Reggia de la Etruschia and it was amazing! Be sure to make reservations if you go, just to be sure.