Super short version: Man, woman, and young teen on rafting trip in remote area trapped above a waterfall with no way down. They write a message on a piece of paper and put it in a Nalgene bottle and send it down stream. Message is found by others, they are rescued the next morning.
So, if you threw a Nalgene bottle over Yellowstone Falls how long would it take it to reach the Gulf of Mexico if it didn't get hung up along the way?