If the thing you look least forward to on vacation is wracking up vicious amounts of debt on your Master Card, then you've come to the right place. I'm here to offer advice on free things to do while visiting San Francisco. Granted, it is not wise to think that you can go on vacation without spending any money and have a good time. However, it is quite possible to be very selective when deciding where to spend your money by having alternative entertainment options that cost little or no money. Rather than a top ten list, which can be…