There's definitely got to be a balance between realism and playability. I like the idea of bits of furniture in amongst the rubble but depending on how many periods you want your ruin to cover, that might be for more generic items like wooden chairs, tables, etc. If it's a building that you could use for Napoleonics through to WWII you're not going to burying metal drums in it, for example.
Buildings don't always collapse inwards either (very often, but not always), particularly buildings that suffer subsequent fire damage. If a building has burning timberwork after initial impact it can expand the timbers and push out external walls, lean-tos, extensions, etc. I've seen the aftermath of this as recently as a few months ago where a timber truss pushed out brick columns and wall plates causing the walls to collapse outwards.