Royal Navy vessels wishing to enter The Port of London are required to give a barrel of rum or wine upon entry as a gift. To whom?

This is one of those fun traditions that has not gone away with time. It dates all the way back to the 14th century. Sure, it could be done away with, but many see it as a way of preserving a piece of history.

In the middle ages, Kings of England tried to assert their control over the City of London. One of the ways they did so was by demanding a gift. They believed they had the right to take tolls from ships sailing on the River Thames. Even today, ships in the Royal Navy are required to hand over a barrel of rum or wine to the Constable of the Tower of London if they want to enter the Port of London.

In order to do his job properly, the Constable had the power to take goods from ships for the sake of the King. In modern times, things have become much more ceremonial.

Typically, the captain of a ship marches a group of officers and sailors, led by a band, to the Tower’s West Gate. There they are challenged by a jailer holding an ax to gain entry into the Tower. They are escorted by men known as “Beefeaters” who wear red and gold dresses.

Of course, other things have been altered over the centuries, too. In the past, oysters, mussels, and cockles were also given as gifts.

(Source)