Can you pack a flask on an overseas flight?

You may pack it in your luggage to check, and you might be able to get it through customs in your carry on luggage. However, you may not legally consume alcohol unless you have been served by the airlines. I'm sure people do it, but they will take it away if you are caught and it will probably stress out your seatmates. Everybody is on edge about flying now and the best thing for all passengers is not to draw attention. Many European carriers have a free drink policy in all classes. USA carriers will charge you a fee. First class drinks are free.