It's hard to miss checkout for fish and a fair amount of beer (10)

'beer' is the definition.
Both the definition and answer are singular nouns.
Maybe you can see an association between them that I don't see?

'it's hard to miss checkout for fish and a fair amount' is the wordplay.
I cannot really see how this works, but
'hard' could be 'h' (abbreviation used in pencil classifications) and 'h' is located in the answer.
'a' is found in the answer.
'amount' could be 't' (T is an example) and 't' is located in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

'of' acts as a link.

Can you help me to learn more?