Okay this is another easy one - most people probably don't even know there are more than one train station in Florence (but there are, like Firenze Rifredi and Firenze Campo di Marte) - so I will stick to the obvious for this favorite.
Also choose to highlight this as a favorite today to mention the new(er) luggage storage area (see photos below). It is located about 100 meters down track 16. If you are facing the tracks, it is the last line on the right. The new sign is sort of small and hidden by an older one at the moment so it is a bit hard to see. The old luggage storage was in the same area but the office was much closer to the terminal part of the building. Not sure why they changed this, but they did.