Minor in Possession in California

My question involves criminal law for the state of: California
One of my friends was charged with a misdemeanor for minor in possession of alcohol.
We were celebrating another friend's 18th birthday. (all of us were 18 years old.) and decided to go to the beach to have a bonfire. We didn't have any alcohol on us when we came, but we had bought cigars. All the firepits were taken, but two men came up to us and offered to share theirs. They had alcohol, and three of our party drank some. The two men left, and we proceeded to sing "Happy Birthday" in an obnoxious way. Right afterwards, two police cars drove over. My friend, who was charged, flicked his cigar in the sand and it happened to land right next to the bottle of alcohol that the two men left. The police officer asked my friend if it was marajuana, and decided that it wasn't, but saw the bottle of alcohol. She asked if we had drank any, and those who had admitted to it. She asked my friend where he had gotten the alcohol, and he lied and told her that he had found it by some other firepit.
She gave him the eye test, and he passed. She did not question the rest of us or charge us with anything. All of us are good students, none of us have gotten in trouble with the law before, except for the friend who was charged, who has only gotten a minor traffic violation.
What is the maximum penalty that he can be charged with?
Is it possible for the rest of us to get in trouble for what happened?
What is a likely punishment for this?
Thank you!

Your friend is looking at a fine of ~$250 and a license suspension of one year.

If you haven't been charged, you're not in trouble, nor will you get in trouble at this late date.