follow the money
Refers to the shameless act of stealthily sneaking along some distance behind a returnables-gatherer who is practicing the toss-across collecting method, and surreptitiously retrieving the bottles and cans that the gatherer has stockpiled on the other side of the road, along with any additional empties that are already on that side. By carefully hanging back far enough behind the collector and therefore staying out of his sight, the opportunist will likely never be observed, and thus the collector will be greeted with just a "barren" roadside all the way when he turns around to start bagging up his laboriously-collected empties on his trek back home again.
I usually try to start out at first light to collect returnables, so that any lazy-a** local delinquents who would want to "follow the money" will not even be awake yet, and thus they will not observe me or know to try following me around town that day to pilfer all my hard work.