Yuletide beverage (3)
'yuletide beverage' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nog that I've seen before include "Noggin the -, cartoon" , "Drink" .)
(Other definitions for eggnog that I've seen before include "Dairy-based drink" , "Xmas tipple" , "spirits in me?" , "Drink of milk or cream, eggs and alcohol" , "warming drink" .)