semi-colons and state abbreviations

Journalists like to drop the comma before the "and" when there are three or more items in a series. But as Mamma used to say, if your friends said jomp off a bridge, would you?

Because the meaning can change if the comma is omitted, I say always use it ... especially in formal writing and documents with legal import. Some twenty years ago, a project I was associated with became embroiled in a several million dollar lawsuit that hinged on whether the contract meant three items , or two (one having a compound name like "block and tackle"). The judge said two and the Contractor earned a tidy profit to provide all three items. The Owner sued the Architect for the added cost, and the Architect was put out of business.

Yes, in your example sentence, you'd need a semicolon before Malibu. As for the abbreviation of Massachusetts, you'll want to stay consistent with the other items in your list -- so MA is the way to go:

I want to sail to San Francisco, CA; Malibu, CA and Cape Cod, MA.

But since the locations of all three cities are pretty well-known, you could also leave out the states, entirely (depending on your audience):

I want to sail to San Francisco, Malibu and Cape Cod.