Mississippi is the only state which does not expressly prohibit the possession of an open container while driving. However, before you hit the backroads with an open can/bottle of your favorite alcoholic beverage, a few things should be considered: First, no matter the scenario, if you are caught operating a vehicle with a blood alcohol content of .08%, you will likely be charged with driving under the influence (DUI). Second, if an officer sees you driving and drinking, regardless of your level of sobriety, you are likely to face the hassle of being pulled over and questioned. Third, some counties and/or cities may have their own prohibition against open containers which could land you in trouble.
As a best practice, it is wise to avoid driving with an open container in the vehicle, and/or drinking and driving (obviously).