Crossword Genius

Subway staples ___come? (5,3,6)

Ross

I believe the answer is:

bread and butter

I'm a little stuck... Click here to teach me more about this clue!

'subway' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for bread and butter that I've seen before include "sandwiches?" , "Food" , "Subsistence" , "earned?" , "A crust" .)

I've seen this clue in the Sydney Morning Herald.
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