I just read an article on the Internet that reported that some French restaurants are permitting customers to leave with the unconsumed portion of the wine in bottles that they purchased with a meal. This is in response to a reported French crackdown on drunken driving. My main surprise was that such a practice had been, until now at least, been, er, not practiced. I'll bet there are a lot of unhappy waiters in France these days.
That got me to thinking what the practice is in other places and how they might vary in the USA from state to state, and how specific laws might affect things. Where I live (Washington State), I have never had a problem taking the unconsumed remains from a bottle that I had purchased at a restaurant. Generally, the waiter will provide a bag for the purpose. I know that, legally, the opened bottle must then be transported in a location that is inaccessible to the driver of a vehicle.
Vino