Last drink of the day? (8)
I believe the answer is:
nightcap
'last drink of the day?' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for nightcap that I've seen before include "Tot, at bedtime" , "drink having sleepy effect?" , "Take before bed or wear in bed" , "Bedtime beverage" , "Bed wear - late drink" .)