Luggage and bags:
Florence is a city you can take a suitcase to. The route from the train station to the Duomo area is all sidewalk, with a little cobblestoned areas, but easily travelled. Plus, it is walking distance.
Clothing/Shoes/Weather Gear: If you intend to visit the Duomo, or other churches while visiting, bring a shawl with which to cover your bare arms and shoulders. Or, better still, buy one from the many stalls, cheap enough.
I always suggest running shoes, or a good comfortable walking shoe. If you have a need for heels, carry them, wear sandles, and change before going into the restaurant.
Toiletries and Medical Supplies: I always suggest Advil, because they are not available in Italy. So, if Migrains are a part of your life, stock up.
Photo Equipment: Lots and lots of photo ops. Bring film, extra memory for your digital, and spare rechargeble batteries. Buy a charger here if necessary. About 12 euro.
Miscellaneous: Florence is so expensive, at least around the Duomo. We were with my mother-in-law who is 78 yrs., so we didn't venture too far from our hotel this trip. (Aug 04) Food is horrendously expensive, and to buy a drink of ordinary pop, expect to spend 3.30 euro. Outrageous, and unnecessary.
If you happen to be heading to Venice first, and travelling in the hot summer months, pick up a fan, but look for the all wood type. Last longer, and quite necessary ladies.
Clothing/Shoes/Weather Gear: When you are visiting churches, be sure not to wear miniskirts or have your shoulders exposed! You can wear spaghetti straps if you bring a shawl or scarf to cover up when you step inside the churches. So I think it is a good idea to bring one along with you or buy one there. Especially if it is summer and warm and you do not want to walk around all bundled up!