Having had a few, unlikely to buy a round (5)
I believe the answer is:
tight
I believe this is a double definition.
'having had a few' is the first definition.
(tight can mean drunk - having had a few drinks)
'unlikely to buy a round' is the second definition.
(tight can mean unwilling to spend money)
(Other definitions for tight that I've seen before include "Well oiled" , "Snug" , "Close-fitting; cramped; mean" , "Drunk; giving little room" , "Squeezed" .)