There is a lot to explore and see in the small town of San Gimignano. This website has a great list of suggested sites and restaurants!

https://www.firenzemadeintuscany.com/en/article/what-see-where-eat-san-gimignano/

Here are a few activities in/near San Gimignano:

Cooking Class

https://www.viator.com/tours/San-Gimignano/Half-Day-Cooking-Class-in-Tuscany-among-the-Chianti-Vineyards/d29096-16521P3

Vineyard Walk & Wine Tasting

https://www.viator.com/tours/San-Gimignano/Vineyard-Tour-Wine-Tasting-and-Lunch-in-Tuscany/d29096-15204P15

Dinner & Wine Tasting

https://www.viator.com/tours/San-Gimignano/Romantic-Vineyard-Dinner-Experience-in-Tuscany/d29096-15204P16

Cheese & Wine Tasting

https://www.getyourguide.com/ulignano-l183582/san-gimignano-cheese-and-wine-tasting-tour-t605850/?ranking_uuid=500ffeeb-0490-4663-b3ff-d9b07372954b

Walking Tour

https://www.getyourguide.com/san-gimignano-l527/san-gimignano-private-and-guided-walking-tour-t411695/?ranking_uuid=a9261817-da59-40f9-a6fb-fad1dc927c07

If you plan on getting to San Gimignano a day or two before the wedding festivities begin, here are a few day trips you could consider to see more of Tuscany:

Pisa - 1hr 15min

Siena - 45min

Florence - 1hr

Volterra - 35min

Bologna - 2hr, a bit farther away, but Bologna is often known for having some of the best food in all of Italy.

Livorno - 1hr 20min, right along the coast of the Ligurian Sea!