San Fran plenty to see, but be careful going on a wander if you don't have a target in mind. The hills are no joke, you'll suddenly be at the bottom of some unpleasant climbs.
Alcatraz obviously a must. Tour is really well done. Book your tickets online and just download them to your phone. Head for clam chowder bowl when you arrive back on the boat. Loads of eating options round the piers in that part of town.
Don't hesitate hopping on the cable cars, some are at busy intersections and they want you on asap. Careful getting off them, big leap down.