Sir, a tab's arranged for those at the drinks counter (8)
I believe the answer is:
baristas
'those at the drinks counter' is the definition.
'sir a tab's arranged' is the wordplay.
'arranged' indicates anagramming the letters.
'sir'+'a'+'tabs'='siratabs'
'siratabs' anagrammed gives 'BARISTAS'.
'for' is the link.
(Other definitions for baristas that I've seen before include "They're skilled in coffee-making" , "Coffee makers" , "People who make and serve coffee" , "Coffee-bar workers" .)