Being a small medival town, there ain't much happening at night. So, what I suggest is to get together with your mates and either do the restaurant thing, or better yet, have a house party!!
My friends and I seemed to have found the correct way to do this...
It´s one of the most romantic things you can do in Tuscany. Stay overnight in San Gimignano and wander around the town.... All the daily tourists are home again and the middle age is nearer than you think. There is not much light in the small streets and you will feel a few centuries back in time sometimes. Lovely!
Dress Code: In november you should have a warm jacket in your suitcase. It can get quite chilly here!