Extravagant expert to enjoy a litre (8)
I believe the answer is:
prodigal
'extravagant' is the definition.
(I know that extravagant can be written as prodigal)
'expert to enjoy a litre' is the wordplay.
'expert' becomes 'pro' (short for professional).
'to enjoy' becomes 'dig' (to dig can mean to appreciate or 'get').
'litre' becomes 'L' (abbreviation).
'pro'+'dig'+'a'+'l'='PRODIGAL'
(Other definitions for prodigal that I've seen before include "This son got the fatted calf" , "overspending" , "reckless" , "Wastefully extravagant" , "Profligate" .)