Cashier accepts note for modest fare (5)
I believe the answer is:
snack
'modest fare' is the definition.
(small amount of food or fare)
'cashier accepts note' is the wordplay.
'cashier' becomes 'sack ' (I've seen this before).
'accepts' indicates putting letters inside.
'note' becomes 'n' (abbreviation).
'sack' enclosing 'n' is 'SNACK'.
'for' is the link.
(Other definitions for snack that I've seen before include "Quick bite to eat" , "Elevenses?" , "Small or huried meal" , "(Eat) a light meal" , "Light bite" .)