By car: from San Francisco to Napa/Sonoma take Hwy 101 to Hwy 37 east. At the split take Hwy 121 north, then north again on Hwy 12 to Sonoma. For Napa, stay on Hwy 121, turning east, to Hwy 29 and turn north.
We don't recommend bus travel to the Wine Country since, on arrival, you'll find inadequate public transportation. However, Greyhound does go to Sonoma Plaza, and there are airport shuttles at both SFO and Oakland airports.
Bicycles, if transported in a box, can be brought to the Wine Country on Greyhound buses for a fee. You can also rent bikes in most of Napa Valley's major towns. Some companies offer guided single- and multi-day bicycle tours through Wine Country.
Bus tours from San Francisco are operated by Gray Lines, which offers a one-day trek that covers both Napa and Sonoma Valleys and includes visits to two or three wineries and a stop to shop and lunch on your own. Golden Gate Transit has daily buses from San Francisco's Transbay Terminal to Santa Rosa. Greyhound has services from San Francisco to Santa Rosa and farther north along Hwy 101.