Light meals NAAFI originally served in bags (6)
I believe the answer is:
snacks
'light meals' is the definition.
(I've seen this in another clue)
'naafi originally served in bags' is the wordplay.
'originally' suggests taking the first letters.
'served in' indicates putting letters inside.
'bags' becomes 'sacks' (sack is a kind of bag).
The initial letter of 'naafi' is 'n'.
'n' placed inside 'sacks' is 'SNACKS'.
(Other definitions for snacks that I've seen before include "Light repasts" , "Light bites such as crisps" , "Light informal meals" , "Small food amounts between main meals" , "Nibbles" .)