Green’s Dictionary of Slang

(US prison) Kool brand cigarettes.

1981		Maledicta V:1+2 (Summer + Winter) 267: In prison, cigarets serve as a universal means of exchange, with a brick being a carton, Double O’s for Kool cigarets, and red head for match.
1997		(con. 1970s) G. Pelecanos King Suckerman (1998) 31: ‘Gimme one of them double-O’s,’ said Russell.
2000		G. Pelecanos Shame the Devil 45: We took that pack of Kools — had to be double O’s ’cause we knew that all the bad brothers smoked those.
2005		R. Cea No Lights, No Sirens 43: [A] pack of Kools, or double Os as they’re referred to.