Don't drop anything in bag (7)

I believe the answer is:

holdall

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'bag' is the definition.
(I know that holdall is a type of bag)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for holdall that I've seen before include "Largish bag" , "Large carrying bag" , "Bag (contents unlimited?)" , "Big bag" , "Large bag (no need for another?)" .)

I've seen this clue in The Guardian.

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