The sort of drill to fill the case (4)

I believe the answer is:

pack

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'case' is the definition.
(I know that pack is a more specific form of the action case)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for pack that I've seen before include "Cards; group of animals" , "Wolves, say" , "Fill (a suitcase)" , "Set, band; carton" , "Fill luggage - wolves" .)

I've seen this clue in The Irish Independent.

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