Green’s Dictionary of Slang

(US drugs) one’s own supply of drugs.

2002		Stoners’ Dict. 🌐 Persy [CA] – Personal supply of pot.
2006		Observer 11 June 9: Would you know what I was talking about if I asked for ‘an ’Enry’ and said, ‘It’s for Percy?’ he asked. ‘It means I want an eighth of an ounce of cannabis for personal use.’.
2012		(con. 1980s) I. Welsh Skagboys 333: If ah’ve kept some percy back then he’ll undoubtedly have followed suit.
2012		Skepta ‘Tour Bus Massacre’ 🎵 You can get thrown in the van / For a Persie.