Take the cable car, ride up and down SF, especially the stretch bewtween fishermen's wharf and union square, be entertained by the 2 drivers onboard and watch them change the direction of the cars at the terminals. 
Try to find the free Presidio Downtown at the Embarcado station (bus stop rather hard to locate), take it to the Presidio Visitor Center and change to the Presidio bus to see the Golden Gate Bridge. Free one.
Don't worry if you lose your in the Presidio, just look out for this friendly, superstar lookalike Muni (no.43?) driver who tries his best to give directions and takes you THERE.
Eat dim sum at Chinatown (siew mai at Hoang Ah, Pagoda St is great but provided u can locate it), then walk up and down the hilly district to burn some calories. Chinatown in SF is like HK in the 70s and 80s. Reminds me of Sheung Wan. Look out for the "Goach" bags
Visit Alcatraz and learn how to escape from the prisons.
Shop at Union Square and especially at Old Navy...catch the weekend sales. I bought 4 pairs of shoes at one goal
MUST go UC Berkeley, talk to some smart people there and not forget to try out the wonderfully tasty gigantic honey oatmeal sandwich from cafe montessori along telegraph ave. Amoeba music is worth a visit
For cartoon junkies, catch the simpsons and the family guy on tv in the evenings. Lose some moral values
Take the F line streetcar to catch a glimpse of the city, then spot some blacks and homeless yelling or maybe fighting along 6th and 7th Market Street, striking crowd...
Go to Ferry Plaza Market if you can spare some time
Must drink Starbucks. Everyone has a cup in their hand, so don't lose out (bring your kiasu-ism with you). Coffee especially comforting in winter (it was 5deg when i went).
Try to meet some new friends on the plane ride to Japan, most of them are Japanese. Remeber to learn some manners and bring them back to Singapore. Will talk about Portland later when i'm in the mood.
