Los Angeles and Southern California can be chilly that time of year. Most likely however your weather will be glorious the entire time. I think just a long sleeved jersey of some sort or a wind breaker would be sufficient. It's not going to be THAT cold, I promise.
I was raised in the L.A. area and never wore jackets in October, but that's just me. Out at sea can be windy, however.
Mexico weather will be very warm and should be quite nice by those dates. The extreme humidity should be gone by then. Tha worst months for humidity are July, August, & September.