Green’s Dictionary of Slang

1. two portions of a narcotic drug, usu. cocaine, laid out in lines for inhalation [i.e. one for each nostril].

1976		R. Sabbag Snowblind (1978) 62: Chop up the crystals, divide the pile into ‘lines’, one for each nostril – call it a one and one – and with a bank note of impressive denomination rolled into a straw ... snort.
1977		S. Kernochan Dry Hustle 45: Murphy dipped the corner of a matchbox cover into his bed-side bag of coke and snorted. ‘You want a one-and-one?’ I shook my head.
1981		H. Gould Fort Apache, The Bronx 221: On top of the booze and the blow [...] even a one and one of this shmeck would put him away. [Ibid.] 314: Chino fumbled around for the vial of coke on the night table to see if he had enough for a one and one to get his head straight.
1983		Grandmaster & Melle Mel ‘White Lines’ 🎵 I need some one-on-one, baby.
1997		Simon & Burns Corner (1998) 311: The touts see all that green and welcome them home in the traditional way, with one-and-one.

2. a dose of one tablet of Talwin (a painkiller) + one tablet of Pyribenzamine (an antihistamine).

2001

ONDCP Street Terms 16: One and Ones — Talwin and ritalin combination is injected and produces an effect similar to the effect of heroin mixed with cocaine.