They used to dump them in unlocked dumpsters but people figured that out and started pilfering the dumpsters. My dad, not poor at all but quite frugal/cheap, somehow heard about this and started taking me as a kid to go dumpster diving with him. It was crazy the amount of food we brought home for those couple years before places started locking the dumpsters. And there were a lot of people driving up and going through them just like us.