You don't have to drink any of the alcohol to be convicted of an underaged drinking offense. The mere possession of it is enough as you can see from SD Codified Laws:35-9-2. Purchase, possession, or consumption of beverage by person under twenty-one years prohibited--Exception--Misrepresentation of age--Violation as misdemeanor.
It is a Class 2 misdemeanor for any person under the age of twenty-one years to
purchase, attempt to purchase, or possess
or consume alcoholic beverages except pursuant to § 35-9-1.1 or when consumed in a religious ceremony and given to the person by an authorized person, or to misrepresent his or her age with the use of any document for the purpose of purchasing or attempting to purchase alcoholic beverages from any licensee licensed under this title.
A class 2 misdemeanor in South Dakota carries a penalty of up to 30 days in jail and /or a $500 fine. That would be your maximum risk if you took this case all the way to trial and lost.
Additionally, for a first offense under the above statute , your license can also be suspended for up to a year, thouth there would be a hardship license available to you. See 35-9-7
In answer to your original question, the particular charge is a strict liability offense -- a zero tolerance crime. If you're under 21 and you've got alcohol in your possession you can be convicted of this crime.
The state does have diversion programs for underaged drinkers which vary slightly from state to state but basically involve fines, community service, anti-alcohol awareness classes and a brief period of supervised or unsupervised probation. At the end of this, if there have been no further problems with the law, the case gets dismissed and would then not give you a criminal record. In order to take advantage of a diversion program, you would have to agree to this almost immediately. Once you turn it down and start appearing before the judge, it is no longer an option. Other non-jail offers would be, but they won't necessarily seal your record.
You do have a potential search and seizure issue. It is not clear why the police stopped you or if he had the authority to search your car. You could challenge the stop and the search, but you would have to choose to try the case and turn down a diversion (and any other) offer. Because the way to challenge the constitutionality of a search is to move for a pre-trial suppression hearing.
The US Supreme Court has said that to determine whether someone's rights are violated, a hearing must be held, as what's proper or not has to be decided on a case-by-case basis according to what a reasonable police officer would do under all the circumstances. These hearings are hard to win, but essentially, the prosecutor would call the police to the stand and get him to explain the stop and the search with a view towards showing that everything the police officer did under the circumstances was reasonable. Then your lawyer (you are a criminal defendant and should have one) would get the opportunity to cross-examine the officer to show just how unreasonable his actions were. The judge would then decide whether your rights were violated.
If the judge determined that the police behavior was unreasonable and in violation of your constitutional rights, the alcohol could not be used against you, and the case would have to be dismissed. If the judge determined that the police behavior was reasonable under all the circumstances, the evidence comes in at your trial, and you'd have no defense to the charge and you'd have already turned down the best deal you were going to get.
As indicated before, you should have a lawyer. He can probably negotiate a disposition where you come out of this without a record. Or, once he hears everything from you in detail, he may think you can win a suppression hearing. Again however, if you lose the hearing you will almost certainly lose the trial. If you lose the trial, you do risk some jail time.
Edited by FranL on 11/2/2010 at 1:00 AM EST