Staying in Sunnyvale, visiting San Francisco 1 day. Which transport pass?

I would be staying in Sunnyvale and will go to SF for 1 day. Which transport pass would be the best ?

I am seeing that one needs Caltrain to go to SF back and forth, and inside SF there are MUNI and BART. Which one should I buy to be most convenient and economical ?

I am new and intend to visit some of the main attractions : Golden Gate, Fisherman's Wharf, Lombard street, China Town, some green space like Tea Garden, and dinner at somewhere downtown. I don't have a fixed plan in mind yet. Sometimes just wandering in interesting neighborhood like Castro.

From this map Neighborhoods it looks like the most interesting neighborhoods are on the center-east.

Since normally long distance trip like Caltrain SunnyVale-SF will be quite costly, I am looking at some day-pass, if any, that covers this part.

Otherwise, your recommendation would be most welcome, since I am amateur to San Francisco.

Does load-as-you-go Clipper card cover all MUNI, BART and Caltrain ?

Thank you.

Edit:

I am confused and concerned. You guys talk about organization of one of the richest and most advanced cities as if talking about "getting permit A38".

To be clear, my itinerary would be : Friday 28th Feb 2020 arriving alone at SFO 2pm, taking BART PR-S SFO-Millbrae, then transfer Caltrain Millbrae-SunnyVale. Friend's house is near SunnyVale station. Saturday 29th, 2 persons SunnyVale-SF wandering visiting whole day in SF, evening around 9-10pm back to SunnyVale. There you are.

What would be your recommendation of transport ticket and solution ? And can the ticket be bought at SunnyVale and SFO ?