At a minimum, everyone in California should have some uninsured/underinsured motorist coverage. Generally, uninsured/underinsured motorist coverage should be the same (or similar) limits to your liability coverage. Uninsured motorist coverage will cover you when you have an accident with someone who does not have insurance but is legally responsible for your injuries.
This type of coverage also applies to hit-and-run situations. An underinsured motorist policy will cover you when you have an accident with someone who has liability insurance with limits that are lower than your uninsured motorist coverage limits. In cases of accidents involving these complicated types of insurance, it is best to hire and experienced firm that understands these issues.