Drink often found in schoolbag (4)

I believe the answer is:

cola

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'drink' is the definition.
(cola is a kind of drink)

I can't explain the rest of the clue.

(Other definitions for cola that I've seen before include "pop" , "Carbonated soft drink" , "Cold drink" , "Fizzy drink" .)

I've seen this clue in The Hindu.

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