My brother in law used to work in an off licence (booze store) so got to know a number of customers, some of which were drug addicts. They would steal from the local supermarket which was right next door. Things like expensive meats, cheese, coffee, spirits, etc. high value products which are easy to shove in a bag or jacket. They then go and knock on the door of anybody they remotely know who lives nearby, ask if they want to buy some cheap goods. Often about 50% off.

I know people who would buy this stuff. It's usually stuff straight from the shop but I suppose you can never say for sure.