The one day passes are only sold at MUNI, there's also Clipper Cards but if you don't know the system it is complicated. Day passes are mostly for tourists, but the clipper cards (like London Oyster cards) are for everyone and that's what they sell at walgreens. We've also just changed over to Clipper so a lot of people including drivers themselves don't know what's going on.

And while MUNI drivers are rude and lack knowledge, a lot of urban transit systems don't sell day passes from individual drivers.

It's a good reminder here, though for we locals to be cognizant of transit needs when visitors ask about sightseeing.

Glad you made the best of your time here and hope you come back!