Generally speaking it's probably the water heater. At any moment it holds approximately 340 lbs of water plus heating apparatus and various sensor systems and sufficient material to both insulate the water from the outside world and to contain a few dozen PSI worth of pressure. Total weight almost certainly exceeds 500 lbs. Anything heavier wouldn't seem to count as an object in the place so much as a part of the place (my cabinets for example won't move easily for reasons beyond their mass). My refrigerator was relatively easy to put into place as myself and a few friends managed it without trouble. Even when stocked, there is perhaps a half dozen bottles of water, roughly the same quantity of soda (generally Mountain Dew or Ginger Ale), small quantities of perishable food stuffs (cheese for example) and a few frozen items along with a few trays of ice cubes. Normally, if I cook a real meal, I go to the store and purchase exactly what is necessary for the job.