There is always "a chance of defending" anyone charged with a crime--no matter how petty. You want to be careful because if the California statute he allegedly violated is criminal, then a criminal conviction could result, so be careful. Try and bargain for a withhold of adjudication versus an adjudication/conviction. Also, be aware that some states will suspens someone's license for a short period of time if convicted of possession. Consult a local attorney for more details.
Consult an experienced local criminal defense attorney for advice specific to your situation.
While it is a crime for a minor to possess alcohol, there could be many situations where there is a defense to the charge. For example:
Did the minor know that the container contained alcohol? Did the minor knowingly possess the container? Was the stop of the minor, or the search of the minor based on probable cause? Did the arrest take place after 10:00PM? Did the officer personally witness the crime?
These, and many other questions could potentially give rise to a defense. For these reasons, consult an attorney you trust. If you cannot afford an attorney, request a public defender when you go to your arraignment.
There is always a chance of defending a criminal charge but you should meet with a criminal defense attorney to discuss the specific facts of this case. Minor in possession does not require driving nor intoxication. It merely requires that the minor posses alcohol and that he knows that he is in possession of it.
If your question is: Is it possible to SUCCESSFULLY defend a minor in possession when the charge is 'just possession', the answer is: Anything is possible. Is it probably, unlikely. With this mear statement no attorney can answer the question. You need to contact a lawyer in your area and go detail by detail to determine if there is a defense.
My answer is for eductional purposes only. For true legal advice, consult a local, experienced criminal lawyer.