Snack in trolley (4)

I believe the answer is:

roll

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'snack' is the definition.
The definition and answer can be both things that one consumes for nourishment as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'in trolley' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ROLL' is hidden in the letters of 'trolley'.

Can you help me to learn more?

(Other definitions for roll that I've seen before include "on which one is regularly successful" , "Swell" , "Bread - list - drumbeats" , "Schedule" , "Bun" .)

I've seen this clue in The Mirror.

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