Any suggestions? What is open and what is there to do?
the town and the towers are really the highlight. all of that will be available to you. the small bakeries and shops will largely be open as well. it is cool, but a whole week there might drive you mad. hopefully you will be seeing more of tuscany during your stay. for me i would stay in siena or florence and visit san g during a day or two. have fun, be safe.
I agree with the previous poster - stay in Florence or Siena, and day-trip to SG. My money would be on Florence, more to do. In the main square of SG there's a gelato place that bears the sign "world champion" - there are a lot of gelato places on that square, but look for this particular one. It is the best gelato we had in Italy. The Fior di Nutella had me in near tears, it was so good!
I was in San G today. The town was putting up its holiday lights across the cobblestone streets. Got some nice photos as it looked rather strange to see workmen on a cherry picker high above those medieval streets!