Green’s Dictionary of Slang

(drugs) to steal.

1989		(con. 1982–6) T. Williams Cocaine Kids (1990) 108: To sancocho is to steal crack, drugs or money from a friend or other person who is not alert, a regular practice in the crack house.
1992		T. Williams Crackhouse 79: Some want to have sex, others want to sancocho, others want to go out on missions.
2001		ONDCP Street Terms 18: Sancocho (Spanish) — To steal.