It sounds like you are charged with both the 18.2-388 charge, commonly called "drunk in public," and with underage possession of alcohol.
The maximum punishment for being drunk in public in Virginia is a $250.00 fine. The underage possession charge is a Class 1 Misdemeanor and carries the potential for a jail sentence and a six-month loss of driving privileges, among other punishments.
You should speak to a lawyer who is familiar with the court where you will be going. There is a first-offender probationary program available for underage possession that may be available to you. In addition, you may have valid defenses to both charges.
In the meantime, go to www.courts.state.va.us and look in the Case Information section for the court where you are to go. If you type in your name you can find out if both charges were brought or just the one.