Fish product is ready to drink? (9)
I believe the answer is:
isinglass
'fish product' is the definition.
(gelatin from fish)
'is ready to drink?' is the wordplay.
I cannot really see how this works, but
'is' is present in the answer.
'drink?' could be 'glass' (I've seen this before) and 'glass' is found in the answer.
The remaining letters 'in' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
(Other definitions for isinglass that I've seen before include "Sis, a sling turns out to be a gelatin" , "Mineral" , "Gelatinous substance from sturgeons" , "[MICA]" , "What's got from fish" .)