Most excellent food one's eaten, nothing wasted (7)
I believe the answer is:
meanest
'most excellent' is the definition.
(mean can mean skilled or proficient )
'food one's eaten nothing wasted' is the wordplay.
I cannot quite understand how this works, but
'food' could be 'e' (E is an example) and 'e' is found in the answer.
'one' could be 'ane' (synonyms) and 'ane' is present in the answer.
This explanation may well be incorrect...
(Other definitions for meanest that I've seen before include "Most cruel" , "Most stingy, like 16" , "of least value" , "Most miserable" , "most squalid" .)