Leave the bags at the left luggage at Pisa airport, take a local bus from just outside the airport up to the Piazza Duomo, then when finished take bus back to airport and pick up bags and car.
Here's a map of Pisa Airport:
http://www.pisa-airport.com/sat/cda/...x.php?idArea=6
On this page, it mentions that the information office also acts as a left luggage office:
http://www.pisa-airport.com/sat/cda/...p;idSection=10
http://www.pisa-airport.com/sat/cda/...x.php?idArea=6
On this page, it mentions that the information office also acts as a left luggage office:
http://www.pisa-airport.com/sat/cda/...p;idSection=10
