Cockroach droppings are made up of all sorts of things that roaches have digested: Food from your cupboards, counters, and drawers. Garbage. Rotting flesh. And dead insects, including the carcasses of other cockroaches.
Cockroaches don’t pee (a not-so fun fact), but instead secrete solid and semi-solid waste. All of which varies in appearance, depending on the size, age, and species of roach you’re dealing with.