Technically the store could give him the boot for sampling merchandise but I doubt they'd bother over a cherry. If you look around the store you will doubtless see street people eating lunch here and there. Most stores don't prosecute that.
No that does not fall under AB109. VC 23550.5 which applies to your situation punishes a felony DUI picked up within 10 years of another felony DUI punishable either by state prison or up to one year in county jail. Your license will also be suspended as an habitual traffic offender for 3 years.
You do need to hire a lawyer or ask for the public defender. That said, it is not necessary that you left the store for the charge to stick. Any act of dominion or control over the store's property all do whether you walked past the cash registers or not. For commercial burglary the People will have to prove that you entered the store with the intent to commit larceny. This is a more difficult burden than is sometims thought.
Juvenile hall has not inferred with your graduation but your behavior certainly has. You are entitled to an attorney in this matter so at your first hearing ask for the public defender to be appointed.
The number would not be written on the bag but the drug would have to be in a police evidence envelope marked with identification numbers and signed by a police officer w/i the chain of custody. If you had the dope and walked across the street with it that's transporting; if it was more than you could personally use than it was for sale. Time to lawyer up.
If the officer did not charge you in the field it is highly unlikely that he will charge you later. Even if he did the DA would have to conduct an investigation before a case could be filed and it is probable that based on these facts your case would be rejected.
Above all do not go to the police station to talk to the cop. Do not call the DA to see if charges have been filed. Do not pay an attorney a pile of money when you probably won't need him anyway.
You should learn that...
You need to be more specific about what comes out on your record. Normally when someone is acquitted of all charges they will still have the arrest on their record and the final disposition. Getting this off your record is difficult. I suggest you contact an attorney about a PC 851.8 petition for factual innocence which, if granted, would seal everything.
My Chicago friend seems unfamiliar with practice in CA. The kind of diversion you are talking about does not require the entry of a guilty plea and will allow him to avoid a criminal record. A guilty plea can only be entered in court so if there are no court appearances and your bf was not arrested he should come out of this with no record at all.