Snack's good chance for tucking into pickled eels (9)
I believe the answer is:
elevenses
'snack's' is the definition.
(I've seen this before)
'good chance for tucking into pickled eels' is the wordplay.
'good chance' becomes 'evens' (good chance in betting).
'for tucking into' indicates putting letters inside.
'pickled' indicates an anagram (I've seen this in other clues).
'eels' with letters rearranged gives 'eles'.
'evens' going inside 'eles' is 'ELEVENSES'.
(Other definitions for elevenses that I've seen before include "tenses found immediately before this?" , "Morning refreshment break" , "Mid-morning snacks" , "Soccer teams" , "Refreshments" .)