This is tricky for several reasons. First of all, what sort of climate are you coming from and what's your cold tolerance for generally speaking someone coming from Florida may well find it very chilly here in November whereas my friends from London generally find it OK. Also, when precisely in November for it's one of those months that can still be autumn at the beginning but is usually pure winter at the end. I remember vividly three years back we saw 20C on 1st November but by the end of the month it was so cold and damp, it wouldn't have surprised if it had snowed. It's also one of (if not the) wettest months of the year in central Italy so you will certainly see rain. Re what to pack? Well definitely either a pair of waterproof shoes or two pairs of outdoor footwear that you can rotate if one gets sodden. Certainly lots of layers and subject to how you cope with cold perhaps even a coat and scarf.
I am from Seattle and was fine last November in a turtleneck sweater, warm scarf and waterproof light jacket (we did have more rain than I expected). Usually wore corduroy slacks.
As Yogi Berra may have said: "Prediction is hard -- especially when you're talking about the future."
And especially when you're talking about weather.
I've been In Florence in November when the weather was perfect -- warm clear days and breezy, cool evenings.
I've been in Florence in November when it was really nasty, with a vicious tramontana wind bringing fighting cold from the mountains.
I've also been there when it rained nonstop. I wasn't there for the tragic flood of 1966, but I was there on a couple of occasions, including 1993, when the Arno came incredibly close to flooding -- with water within a foot or so of the tops of the walls along the lungarni.
Remember statistically Florence gets more rain in November than does London.
But statistics can lie.
In short, be prepared for the best and worst.
Obviously, we don't know where you're coming from. If you don't mind packing, bring enough clothing to do some layering if it's cold, and bring foul weather gear in case it's raining non-stop.
Otherwise, bring money for buying additional clothing -- and perhaps additional luggage -- in Florence. It's not the worst place in the world for doing both of those.
As does Rome! I was once stuck next to an Aussie guy on a long haul flight and all the way back to Rome he couldn't stop banging on about it. London-born I was incredulous but later discovered it's true. Too weird for words.
Check the forecast just before you pack, and as late as possible. And yes, layers are the answer to keeping warm. I had a vest-coat to wear over long sleeved tees, as I warm up easily, and this was fine in mid October.
"Check the forecast just before you pack, and as late as possible."
Our experience with weather forecasts in Florence over the years is not good. It's become something of a joke. For example, last winter, we got predictions every day for non-stop rain, and we had at least partly sunny days day after day.