Since you're restricting yourself so much, you don't have many options. One opportunity, although a shitty one, is to find a 24-hr gym with treadmills and get a

Since you're restricting yourself so much, you don't have many options. One opportunity, although a shitty one, is to find a 24-hr gym with treadmills and get a membership, make a platform for your laptop that can hang onto one of the treadmills to use as your work 'desk'(can't get kicked out if you're 'exercising'), you now have a place to work/shower/bathroom, and then you can sleep in your car (which is probably illegal there so find a good parking spot!). I guess it just comes down to how set on being in SF and not giving up equity you are.