Probably nothing unless you were clearly not able to take care of yourself. They could charge you with public intoxication, but it would have to be pretty bad. But realistically, you are in a car. So, even if you were sloppy drunk, the police wouldn't bother charging you with anything. They have already caught a bigger fish, so they wouldn't bother with you realistically. Just send you on your way, and have someone pick you up. They may send you to the hospital if you have alcohol poisoning, but realistically, they would just keep you until you sober up and then you can go home. Even if the police did charge you with something, the prosecutor would probably turn the case down anyway
You have to understand, for the police to file a police report and expend time to arrest you, and then submit the report to the D.A., and then the D.A. having to review your case to determine if they are going to file public intoxication when you are just a passenger in a car and the person driving is DUI? Waste of time and expenses. Public intoxication isn't even priorable. Its generally worthless and a waste of time, and the police are not going to waste time on that unless they really think that the person is a danger to himself or others.
So you can relax. Nothing will happen. Happy Thanksgiving!