Necessary funds enclosed in top half of wallet? (11)

I believe the answer is:

wherewithal

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This might be a double definition.

'necessary' is the first definition.
(I've seen this before)

'funds enclosed in top half of wallet?' is the second definition.
'wherewithal' can be an answer for 'funds' (thesaurus). I'm unsure of the 'enclosed in top half of wallet?' bit.

Can you help me to learn more?

(Other definitions for wherewithal that I've seen before include "The money required for a particular purpose" , "Needed cash" , "Means" , "Essentials" , "Resources" .)

I've seen this clue in The Times.

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