My understanding is that the ancient custom was to pour out a
sacrifice of wine, called a libation, to the appropriate god. For
boats, that would have been Poseidon, and one would have poured the
wine into the sea, The later business with the bottle probably came
about for the sake of news photographers and as a way for latter-day
monotheists to mock the practice without *quite* abandoning it.

For an airplane, I think the equivalent practice would be to release a
bunch of helium balloons to Aeolus, the minor deity in charge of the
four winds.

Don