Invigorating snack item (5)
I believe the answer is:
crisp
This clue is a double definition.
'invigorating' is the first definition.
(I've seen this in another clue)
'snack item' is the second definition.
(I've seen this before)
(Other definitions for crisp that I've seen before include "Crunchy; fresh" , "food in packet" , "Snappy" , "Firm and fresh or easily crumbled" , "Strong and wiry" .)