Not to mention that this is quite small city so even walking is not too big of a problem.
I live in New York City.
On a weekday, the last Caltrain train out of San Francisco leaves around midnight. The next one does not leave until 5 AM.
In NYC you have several trains going out in that time period, whether you're going to Long Island, New Jersey, Westchester or Connecticut.
gonna leave that right there as testament to your credibility
MUNI covers most of the city, goes frequently and is inexpensive. I use buses everyday to commute and to get around the city and find them surprisingly good.
I ride my bike as my primary way of getting around. It's way faster than taking the bus (MUNI average speed is something like 8 mph) and I can leave work after 7:30pm (the time of the last convenient bus).