Last year I was a JFK-LHR which was subsequently delayed for 4 hours. I opened a bottle of Johnny Walker Green and drank some of it with 3 other stranded passengers. When we got on the plane, we continued drinking (while asking for soda's or ice) until there were 3 fingers left in the bottle. The FA mentioned that legally we weren't allowed to pour our own liquor on the plane because of the aforementioned cutoff reasons. Subsequently, one passenger put down a $100 and said "we'll take a bunch of dewars...and let me know when we're cut off". $100 worth of dewards later, we all just went to sleep.