Merry, due to a combination of pourboires and early closing (5)
I believe the answer is:
tipsy
'merry' is the definition.
(I've seen this before)
'pourboires and early closing' is the wordplay.
'pourboires' becomes 'tips' (I've seen this in another clue).
'and' is a charade indicator (letters next to each other).
'closing' says to take the final letters (the letter which ends or closes the word).
The last letter of 'early' is 'y'.
'tips'+'y'='TIPSY'
'due to a combination of' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for tipsy that I've seen before include "Slightly drunk" , "1 over 8" , "Merry, squiffy" , "Woozy" , "Rather drunk" .)