‘Getting your/my/a bag’ is also now modern slang for … bringing in some income for yourself.

Like if you recently got a job, and someone said ‘hell yeah, get your bag!’, that would be an endearing way of congratulating you on your new income or revenue stream, basically.

I am not entirely sure how the modern etymology works, but it is likely related to older, archaic phrases like ‘bag of coin’ that you mention… in some way.