Red wine, small amount, but guy needs it (4,3)
I believe the answer is:
tent peg
'guy needs it' is the definition.
(a guy is a rope fixed to a tent)
'red wine small amount' is the wordplay.
'red wine' becomes 'tent' (type of Spanish wine).
'small amount' becomes 'peg' (a non-specific amount of alcohol).
'tent'+'peg'='TENT-PEG'
'but' acts as a link.
(Other definitions for tent peg that I've seen before include "used to make a guy secure" , "Securer for marquee" , "What guy is steadied by" , "A guy could get attached to that" , "one often found pinning a guy down" .)