Hometown of Renaissance, one of the most beautiful cities in the world, Florence is worth at least a full weekend (even if the more the best!). Just leave your car and the idea of using it and enjoy the pleasure of a long walking tour through the historic centre: start with the Duomo(Cathedral) and Brunelleschi’s ingenious and noble dome for a panorama across the city, then admire the close baptistery, its mosaics inside and the massive bronze doors outside, walk towards Piazza della Signoria and Palazzo Vecchio. Just one minute walk you have the Uffizi (be aware you are going to spend the rest of the afternoon with Giotto, Botticelli, da Vinci, Michelangelo, Raphael, Caravaggio, and Titian). Not far there is Ponte Vecchio with the beautiful shops, the Pitti Palace and the Boboli Gardens.
You are in Italy, in Tuscany (even better!) so take your time and enjoy the sites and everything is on your way.
Florence is also worth visiting for shopping and food: spend some time shopping in the beautiful boutiques of Via Tornabuoni and the neighboring streets and experience some of the best food and wines in Italy.