Nailhead probably has the best advice about just keeping your mouth shut, but...

MMJ is legal in California and there isn't a damn thing LEO's can do about it. Make sure you have a copy of your scrip in your wallet, your glove box etc. If questioned, produce your prescription then keep your mouth shut.

Under California's "Implied Consent Law", you must submit to a breathalyzer test if a LEO demands that you do so. Breathalyzers can't measure thc - you know this, the police know this... Draw your own conclusions.

As far as California's law on the number of plants goes - it makes no sense. It says "... 12 immature OR 6 mature plants..." So ya grow 12 plants and when they reach the point of maturity you kill six????? It makes no sense, but that's the way the law is written.