I always see it on movies where a person is lost on an island and asks for help by sending a message inside a bottle. With enough luck the bottle will reach someone and help the stranded person. Are there any records of this actually saving anyone?
Yes, during the Meermin Slave Mutiny the crew communicated with onshore authorities while the ship had been taken over by slaves. The message said:
Although we trust in the Lord to save us we kindly request the finder of this letter to light three fires on the beach and stand guard at these behind the dunes, should the ship run aground, so that the slaves may not become aware that this is a Christian country. They will certainly kill us if they establish that we made them believe that this is their country.
For context, the slaves did not realize that they were off the coast of South Africa, and instead imagined they were nearer Madagascar, where they intended to go after the mutiny. The fires were lit and the crew saved, though they were demoted.
One of Scotland's most remote islands, St. Kilda, used to have a small population of people living on it, almost completely isolated from the rest of society. They spoke Gaelic, lived off seabirds, kept sheep, and produced tweed. There were a couple of occasions where the island was near to starvation, following a bad winter.
"The St Kilda mailboat was a romantic invention of visitors to the island. The little wooden vessels attached to an inflated sheep's stomach did, however, convey messages to the mainland. On more than one occasion this saved the islanders from starvation"
This is from Tom Steel's 1975 book The Life And Death Of St. Kilda: The moving story of a vanished island community.
The little mailboats were pretty reliable and would usually end up on the mainland, but on occasion they would be carried over to Norway. The whole history of this island is really fascinating. They had a completely unique culture, a lot of which was destroyed by the introduction of the Church of Scotland to the island. Their main communication was with passing steamboats who would carry mail to the mainland for the islanders, and eventually they gained a Royal Mail boat. They also lit fire beacons if they needed to urgently attract the attention of passing ships.
More on the mailboats from the St Kilda official website apparently they were more of a tourist attraction than used for real distress. But the first usage was of distress.