A case of champagne? Great! (3)
I believe the answer is:
ace
'great' is the definition.
(ace can informally mean very good)
'a case of champagne?' is the wordplay.
'case of' suggests removing the centre (outsides of).
'champagne' with its centre taken out is 'ce'.
'a'+'ce'='ACE'
(Other definitions for ace that I've seen before include "Playing card with single spot" , "Single unit on playing cards" , "'wicked'!" , "Player who excels" , "smashing" .)