Full amount of small drink as a loss leader (5)
I believe the answer is:
total
'full amount' is the definition.
(I've seen this before)
'small drink as a loss leader' is the wordplay.
'small drink' becomes 'tot' (I've seen this in another clue).
'leader' suggests taking the first letters.
The first letters of 'as loss' is 'al'.
'tot'+'al'='TOTAL'
'of' acts as a link.
(Other definitions for total that I've seen before include "French oil and gas company" , "Come to" , "Whole, complete" , "Entirety" , "The whole number" .)