Sorry, the claim that "out of pocket" has this alternate, non-financial definition going back to the 1940s is entirely unsupported.

There are four references to "out of pocket" in the book, according to Google Books. All of them have to do with money. https://books.google.com/books/about/Cassell_s_Dictionary_of_Slang.html?id=5GpLcC4a5fAC

If you look at the 50 Cent lyrics in context, they're saying that crack money has slowed down, so the "bitch" is paying out of pocket. https://genius.com/50-cent-in-my-hood-lyrics

Crack money slow so you know niggas is trippin' (Yea!)

Shorty down there on that Queens tracks takin a whippin'

Sheeit, bitch get out of pocket, she need some discipline

Peep the fiend shootin diesel in his arm in the alley

Edit: on reflection, I'm not sure I understand the lyrics well enough to say which way he means "out of pocket" to be taken.