While it is important to keep in mind that slang and speech in California are in constant flux, some words are good to know. At the very least, knowledge of local lingo will allow visitors and recent transplants alike to avoid being left in the dark as conversation whirls around them.
The “Nutrition Facts of Pure Bay Area” are not completely accurate, but the most necessary word to know is hella. Hella, nearly synonomous with “very”, or “a lot of” as when my 70 year-old hippie mom said, “there was hella traffic.” Or, when my sister says that she was “hella hot all day” after a heat wave. At one point, there was a movement to designate hella as 10 to the 27th power.
California slang has its own wikipedia entry (not the most reliable), but there are other resources as well. Real Life English offers 17 California slang terms and claims the “more slang you know, the easier it is to connect and make friends with native speakers.”
Even Business Insider has their own list of “12 Sayings only People from California will Understand.” Once you understand how to use “hella,” the rest is hella easy.