Eat everything because shiner is unavailable (6,3)
I believe the answer is:
polish off
'eat' is the definition.
(I know that polish off is a more specific form of the action eat)
'everything because shiner is unavailable' is the wordplay.
I cannot really see how this works, but
'is' is found in the answer.
'unavailable' could be 'off' and 'off' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for polish off that I've seen before include "Finish completely - kill deliberately" , "Use varnish remover to get this" , "Consume (something) quickly" , "defeat" , "Eat up" .)