can't help I'm afraid but welcome to HT and have a great holiday!

Bon giorno Mr Dublin, I think I can help with your querie, I know of two good sized supermarkets in Pisa one is across the Arno over the Ponte Mezzo, if you go down the Corso Italia as if you were heading towards Pisa Centrale railway station there is a big supermarket on the left down a side street, there is also a huge hypermarket near San Rossore nature reserve and The Pisa San Rossore railway station this isn't to far from The Terra De Miracole where the Tower, the Duomo and Campo Santo is etc, however if you want fresh groceries there is a daily produce market called the Piazza delle Vettovaglie Market which is a excellent daily food market just of Via Borgo Stretto that sells fresh fruit and veg, fresh bread, cheeses, salamis etc, hope this info is helpfull to you.

Buono fortuna
Sliema2