It's vital swimming in rough sea to look forward with relish to good food (8)
I believe the answer is:
salivate
'look forward with relish to good food' is the definition.
(someone might salivate in anticipation of food)
'it's vital swimming in rough sea' is the wordplay.
'swimming' indicates an anagram.
'in' indicates putting letters inside.
'rough sea' becomes 'sae' (I am not sure about this - if you are sure you should believe this answer much more).
'vital' with letters rearranged gives 'livat'.
'livat' put into 'sae' is 'SALIVATE'.
'to' is the link.
(Other definitions for salivate that I've seen before include "Drool" , "Water at the mouth" , "Produce moisture in mouth" , "Make mouth moisture in aestival manner" , "Become moist in mouth" .)