Green’s Dictionary of Slang

1. (drugs) milk sugar, commonly used to adulterate heroin.

1967		Maurer & Vogel Narcotics and Narcotic Addictions (3rd edn).
1969		R.R. Lingeman Drugs from A to Z (1970).
1989		(con. 1939) Courtwright & Des Jarlais Addicts Who Survived 116: When I first started shooting heroin they were cutting it with bonita, and coke with epsom salts.

2. (drugs) heroin [may be misreading of sense 1].

2001

ONDCP Street Terms 4: Bonita (Spanish) — Heroin.