From OED.com

[Wilson Gray]

http://oed.com/view/Entry/187490

1970   L. B. Montgomery in S. Terkel Hard Times v. 377   They had Blue
Monday parties, the sporting people... If they'd been hustlin'
anything,

_they'd be poppin'_,

buying moonshine, having fun, on Monday.

http://oed.com/view/Entry/147790?rskey=IgWxPM&result=15&isAdvanced=false#eid

 f. U.S. slang. To pay (for).

1947   W. Motley Knock on Any Door 169   He might _pop (for)_ the drinks.
1959   R. Bloch Big Kick in Blood runs Cold (1961) 218   He didn't
_pop_... I said we were leaving..and all he did was smile.
1968   L. J. Braun Cat who turned on & Off (1969) xxi. 182   Hell. I
didn't buy you anything, but I'll _pop (for)_ lunch.
1991   J. Phillips You'll never eat Lunch in this Town Again 533   The
deal goes down at Lorimar and we actually get them to _pop (for)_ Anne
Rice writing a ‘bible’ for a series of movies.

What does

_poppin'_

mean, in

"… they'd be poppin', …"?

"… they'd be payin' (for), …"

as in,

"…they'd be payin' (for), buyin' moonshine"?

That is, there's a kind of stutter by the speaker? Bloch 1959 (1961)
is too incomplete for me to tell whether that's what's going on, here.

--
-Wilson
-----
All say, "How hard it is that we have to die!"---a strange complaint
to come from the mouths of people who have had to live.
-Mark Twain

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