The kelp is Pterygophora californica, sometimes known as Walking Kelp.
The sea star is a bit more challenging. Here's a close-up:
It looks like a species of Pisaster to me, with five fairly stubby arms. There are 3 species of Pisaster in this area. The habitat — rafting on kelp — probably isn't that useful as a clue to the species identification because I'm guessing all three Pisaster species could end up in that circumstance.
This individual was very small, ~5 mm across. And it looks very similar to juvenile Ochre Sea Stars (Pisaster ochraceus) that we're familiar with in the rocky intertidal zone on the outer coast (see photo here). But when I thought about it, I realized that I wasn't completely sure how easy it would be to tell the three species of Pisaster apart at that size. They're very easy to separate as adults, but I don't know when they start to differentiate. Does anyone? It would be fun to know! At what size do Short-spined Sea Stars turn pink? When do Giant Sea Stars develop blue rings?
Here are links to Ochre Sea Star (Pisaster ochraceus), Short-spined Sea Star (Pisaster brevispinus), and Giant Sea Star (Pisaster giganteus) adults.