Unironically you actually can make money collecting bottles in Germany. We have a system called "Pfand" (you pay an extra fee when buying the (water) bottle, but get it back in the store when you return the empty bottle). Its 8 cent per beer bottle, 15 per water bottle and 25 for some plastic bottles. Cans apply too, e.g. RedBull etc.
Especially on weekends it is making sense to collect them if you walk around down town when its early morning. Or other highly frequented party locations. But expect competition.