Ok here's the deal, and here's what you can pretty much expect to happen...

If it is a first offense you can plead Nolo, basically means that you are saying you are guilty but you don't want it to do on your record. If it's a DUI you cannot plead Nolo. You can only plead Nolo once every five years so use it wisely. If you don't think that you are going to get into trouble in the next five years then by all means go for it.

If you got the Minor Possession through consumption(meaning you were drunk in a car or elsewhere underage but you weren't driving) then you will be on probation for at least a year, you will have your license suspended for at least a year without the ability to get a to/from work/school/church permit, 40+ hours community service, and also you will have to take the DUI Risk Reduction classes. You can expect about $600 give or take a couple hundred in fines and you may have to serve a little extra time in jail.

Now this depends on the judge too. Some judges couldn't give two shits about you or your situation and some feel sorry and are good judges pof character and can tell which kids know what they did is wrong, and that they won't do it again.

The mandatory time spent in jail for most offenses of this nature are 48 hours. So this means if you spent less you get to go back until you have served the 48 hours.

If you have any other questions then just pm me I know a lot about this from personal experience and because I am a Criminal Justice/Psychology major.

EDIT:
YOU CANNOT GET A WORK/SCHOOL DRIVING PERMIT FOR ANY DRINKING RELATED ARREST UNDER THE AGE OF 21