Transportation
Wedding Ceremony and Reception
One shuttle each will leave the Hotel Rex and the JW Marriot at 5:00 PM on Saturday to "get you to The Legion on time." If for some reason you miss one of the shuttles, you should take a taxi.
Shuttles will leave the reception at around 11:30 PM and drop-off at both hotels. You won't want to miss the last returning shuttle since getting a taxi to come out to that part of San Francisco late on a Saturday night means at least a 30 minutes wait, if you can get one to come at all. Maybe we'll make checking the restrooms before the last shuttle leaves a Best Man duty? I'm sure he'd love that.
General
Assuming you are staying in San Francisco (hopefully at the Hotel Rex) and unless you are leaving the city to explore the Bay Area, there really isn't any need to rent a car or anything like that. You can walk and catch cabs in Union Square pretty easily, not to mention Muni. Don't forget the mildly useful, though thoroughly entertaining, cable cars. If you want to visit Oakland, Berkeley or go to the San Francisco Airport (SFO), BART (our pseudo subway system) is always a good option, too. However, if you are heading to Marin, wine country, the South Bay, etc. you'll need to get a car and partake in our lovely freeway system.