I basically have a file for AutoCAD and Rhino that has all sorts of furniture and objects in standard European sizes. It also features other stuff like special drawing marks, hatches, styles, standard architectural details, and stuff, that I’ve compiled over the last few years. I basically copy and paste from there. These are 2D drawings in top and side views for two-dimensional plans (elevations, sections, details).
For 3D, I have a folder with the standard designer furniture (Eames, Corbu, Ikea, etc.) and various objects (lights, gadgets, etc.) that I can use for very basic arch-viz setups. I’ve bought some, got some from colleagues and friends back at university, even modelled some myself, and downloaded others from various sources.
I don’t do traditional (raytraced) renderings, so simple, untextured 3D geometry mostly does the trick.
Furthermore, I have various Grasshopper and Python scripts for quickly pumping out basic cabinets, railings, stairs, kitchens, sofas and other easy-to-parameterize objects in various sizes and shapes.