Sandwich filler it's a relief to save (5)
I believe the answer is:
bacon
'sandwich' is the definition.
The answer and definition can be both things that one consumes for nourishment as well as being singular nouns.
Maybe you can see a link between them that I can't see?
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bacon that I've seen before include "Cut of pork" , "English breakfast staple" , "Author" , "Cured meat from pig" , "Food that can be streaky" .)