what does "roll bones"mean?
Jake leaned forward in his chair. After a pause he said somberly: ‘My friend, they had stole the fifty-seven dollars and thirty cents from the treasury to buy uniform caps and free Saturday suppers. I caught them sitting around the conference table, rolling the bones, their caps on their heads, and a ham and a gallon of gin in easy reach.’

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Answer

I researched a bit and discovered that "to roll the bones" means "to roll the dice/dices". That's because in the old times they used to make dices from bones. So they were probably playing some game?
P.S.: you can even see this reference in this Rush album cover: https://upload.wikimedia.org/wikipedia/en/4/4c/Rush_RTBsingle.jpg