If you're looking to do a little shopping or just want a nice place to walk around or grab a meal, there are plenty of options in the Stanford Shopping Center. If you're staying at the Sheraton, it's a quick Uber ride or walk to the outdoor mall.
If you're interested in exploring the coast, Half Moon Bay is a beautiful beach area for an afternoon picnic or walk on the beach. For those not from California, keep in mind that Northern California beaches are not typically warm. It's usually 10-20 degrees cooler on the coast.
A great walk/hike up a paved path with beautiful (and foggy) views of the Bay. Parking can be tricky, but it's a great, convenient way to get in some activity while you're here! (Unfortunately, the Dish is closed for maintenance the week of our wedding.)