Drink with royal backing (5)
I believe the answer is:
lager
'drink' is the definition.
(lager is a kind of drink)
'royal backing' is the wordplay.
'royal' becomes 'regal' (synonyms).
'backing' is a reversal indicator.
'regal' written backwards gives 'LAGER'.
'with' acts as a link.
(Other definitions for lager that I've seen before include "Light beer needed" , "Local offering" , "Tipple" , "Regal kind of beer" , "Pilsner, for example" .)