What is the "cup o' kindness" referred to in "Auld Land Syne?"?

Answer 1

In Scotland it was a custom to share a cup of whiskey with friends when they were parting. Sometimes this is called a "Stirrup Cup" because they wouldbe on their horse ready to ride off and the host would bring the parting guest a drink when he was just at the point of leaving.

Answer 2

Robert Burns, the Scottish poet who wrote "Auld Lang Syne" would refer to the "cup of kindness" as whisky.
It means "water of life" or uisge baugh" (pronounced "ish'ka'ba'ha") as it is said in gaelic.