36 CFR § 4.14 - Open container of alcoholic beverage.
(a) Each person within a motor vehicle is responsible for complying with the provisions of this section that pertain to carrying an open container. The operator of a motor vehicle is the person responsible for complying with the provisions of this section that pertain to the storage of an open container.
(b) Carrying or storing a bottle, can or other receptacle containing an alcoholic beverage that is open, or has been opened, or whose seal is broken or the contents of which have been partially removed, within a motor vehicle in a park area is prohibited.
(c) This section does not apply to:
(1) An open container stored in the trunk of a motor vehicle or, if a motor vehicle is not equipped with a trunk, to an open container stored in some other portion of the motor vehicle designed for the storage of luggage and not normally occupied by or readily accessible to the operator or passengers; or
(2) An open container stored in the living quarters of a motor home or camper; or