derived from the phrase "halves (1/2's) on a bag" which is used to describe the action of more than one individual purchasing a parcel of pharmaceuticals, usually evenly distributing money for said purchase.
in other words, goin half on a dub.
"hey home slice, wanna go ham on a bacon tonight? I've got 10 bucks."
other similar phrases might include:
"ham on a bagel"
"ham on a biscuit"
Last week I was sitting off to the side with my girl at McDonald's in the morning and she pointed under the table. Next thing you know, I'm down there eating a Bacon McMuffin.