22 ounces of liquor.
Despite what a previous entry wrote concerning alcohol, a "double duce" is, in my predominantly black neighborhood, 22 ounces of liquor, (rather than 40). A "40" is a "40" no matter what, and the "double duce" is nearly half that amount.
Two people sharing a smokeable item, most often a cigarette.
If one person is smoking a cigarette, his/her friend might say, "Gimme the duce", meaning, "Share that with me?"