the last hit of a cigarette (or the last of anything for that matter). comes from the plight of those incarcerated in jail and how desperate they are for a square - sometimes picking one up off the ground if they see it has even the slightest amount of tobacco left.
"i'm trying to quit smoking, could i just hit the jailhouse off your cig?"
"damn that toblerone
looks good as hell, can i take the jailhouse off that?"
"before you cache
that bowl, lemme try and hit the jailhouse."