Most building debris and household junk is fine to load. The main limits come from Illinois rules on what landfills can take.
The Illinois EPA keeps several items out of landfills altogether. That list includes appliances, electronics, lead-acid and lithium-ion batteries, products with mercury, motor oil, oil-based paint, tires, and yard waste. If one of these ends up in your dumpster, it has to be pulled out before disposal.
Hazardous waste, liquids, paint, solvents, fuel, and asbestos can't go in a standard dumpster either. Peoria County runs a household hazardous waste program for leftover chemicals.
Brush and leaves are a common surprise. Because yard waste is banned from Illinois landfills, keep it out of a mixed load and ask about a separate option.
Before you load anything you're unsure of, check with your account manager.