The number one most important coverage by far is Bodily Injury and Property Damage Liability.  This is not a coverage to short change in the interest of saving money.  If you cause an accident and put someone in the hospital for a week, a month or cause the death of another person, how much might you be sued for?  Think it is limited to your assets?  Think again, if you are found negligent and lose a lawsuit but do not have enough insurance and have limited assets, you could be paying over a period of years to satisfy the judgement.  Buy PLENTY of liability coverage on your California Auto Insurance policy!  No less than 100/300/50 but give serious consieration to higher limits than that and/or an umbrella liability policy that can add $1,000,000 to whatever you purchase. 

Second in importance is uninsured motorist bodily injury.  This is to protect you and your family from injury sustained in an accident with someone either 1) not carrying any insurance or 2) carrying very low limits.  Don't skimp here either.  Best idea is to match whatever your bodily injury liability limit is. 

Medical payments is not meant to take the place of a good health insurance plan.  Many companies only provide up to $5000 or $10,000 for medical payments.  This coverage is for injury sustained by you or the occupants of your vehicle.  Depending on the details of your health plan from 1,000 to 5,000 should be enough usually. 

If either due to a loan on your vehicle or the value of your vehicle you choose to purchase physical damage coverage (collision and/or comprehensive) consider at least a $500 deductible to save dollars here (at least on the collision).  This is a good place to look at saving money.  And, if the car does not have a loan and has dropped to a fairly low value, consider removing collision and/or comprehensive altogether.  If you lose a $4000 car due to an accident or theft then you are out $4000.  If you cause serious injury to someone else and carry low liability limits what might you lose in a lawsuit?  Could be catastrophic! 

Finally there the miscellaneous coverages including towing, rental reimbursement, diminishing deductible, replacement cost and person effects.  Some of these are nice to have but make sure you have first loaded up appropriately on the liability and uninsured motorist before tacking on the extra expense of these coverages.