Most building and household debris is fine to load. The limits come from Maryland law, from Montgomery County's recycling rules, and from what the receiving site will take.
Maryland has banned tires from landfill disposal since the mid-1990s, so they have to be kept out and handled separately. Separately collected yard waste is also barred from disposal in Maryland and belongs in the city yard trim stream instead.
Hazardous waste, liquids, paint, solvents, fuel, used oil, and asbestos cannot go in a container anywhere. Medical waste has its own route under the City code and cannot be set out for collection.
Montgomery County then adds the rule that catches contractors out. Cardboard and scrap metal, including pipe, sheet metal, rebar, fencing, and metal appliances, are mandated for recycling, and a construction project generating any amount of them has to separate them and deliver them to a recycling facility. The county enforces that with citations and fines, so it is worth planning for.
Not sure about an item? Ask your account manager before it goes in the container.