Normal construction and household debris is fine. The limits come from what the Casper landfill is allowed to bury and from the hazardous waste rules the Wyoming Department of Environmental Quality writes.
The landfill cannot bury batteries, appliances, metals, fluorescent tubes, hazardous waste, electronics, used oil, or tires. Anything on that list has to be declared at the gate, pulled out of the load, and taken to its own area, so it is far easier to set those items aside before the container is filled. Casper also keeps electronics and scrap metal out of refuse containers altogether and asks owners to drop them at the landfill themselves.
A few things are turned away outright: material holding freon liquid, live ammunition, fireworks and other explosives, friable asbestos that is not properly contained and declared, and anything the state counts as hazardous. Paint, solvents, fuel, and other liquids stay out of a standard container too.
Households can take their own hazardous waste to the special waste building at the landfill at no charge, and the city recycles batteries there for free. Commercial hazardous waste is not accepted there, so a contractor needs a different route. Refrigerators and freezers must have their doors taken off before they move.
If an item has you guessing, ask your account manager before it goes in the container.