When headed to California, all you need are a few shirts to casually throw on, funky sunglasses (cheaper here), and fun shoes. It's all about being relaxed and chic in Cali, so don't be afraid to throw some neon (this shirt) into the mix to stand out.
I may not be a swimsuit guru, but I swear by J.Crew and Anthropologie. The swimsuits always are fashionable and fit well- plus the colors never fade.
In California, stay feminine or funky (yes, the word shows up again)! I'm obsessed with embellished jean shorts (here), scalloped shorts (here), and colored jeans.