Bud, you obviously haven't been paying attention, have you? Jimmie was crackin' corn!!!

Having given it a little thought, very little in fact, I would go with the thought that he was opening a jug of corn whiskey. The line, as I recall goes, "Jimmie crack corn and I don't care, the master's gone away" Given that the slaves were probably not allowed to drink, other than what they secretly brewed for themselves, we find Jimmie, after the master's demise "cracking corn" and the narrator of the story doesn't care because nobody's around to punish Jimmie in mourning his master.