October & November are open enrollment months for health benefits. If you are employed at a company with benefits, this is the time to make any needed changes. Typically, you cannot change your benefits during other months of the year unless you have a qualifying event such as a new baby or a change in marital status. Review your most recent financial plan and see if there are any recommendations regarding your benefits. You may need to obtain additional life insurance or start utilizing a flex spending account (FSA).
If you have coverage or are looking for coverage through Covered California, this page has everything you need with regards to open enrollment (start date is November 1 for 2016). Open enrollment for Medicare starts on October 15 for 2016 (here is more information). Enrollment for Medi-Cal is year-round.