You may drink alcoholic beverages in a vehicle on a public highway:

It is against the law to consume or possess any alcoholic beverage while on a public road or sidewalk. Additionally, storing an open alcoholic beverage container in an area of a motor vehicle normally occupied by the driver or passenger is prohibited on any public road.

• As long as you aren't driving.
• If you are riding in the back seat.
• If you are riding in the back of a pick-up truck.
• Under no circumstances.