On the ground set an old gondola body, torched open, and/ or with seperation walls added etc. , to form bins. It's prototypical in a way, fills space now, and you can slowly fill them as you find things that work out.
Old broken loco shells can be hacked upfor larger pieces that can eat space, a pilot, cab, dome, or truck or two set near the wheel pile.
If you eat out a lot , skewers, or tooth picks of assorted types can give you iron bars, pipe, etc in different sizes and shape to add to/around the big stuff or piles.
Models or toys with a straight engine vs a V8, even in the wrong scale can easily pass for an industrial block.
Same for wheels, tires and internal gears from wind up toys (by the wheels since not many have keys. ) Off the vehicle, their scale is variable by the things around it -. E.g. Industrial loader tire or an off-road pickups? With a RR truck nearby it's a loader's tire.
Stop at a brake shop and ask for scrap tube for a pipe pile ( new scraps.)
Flea market misfit toy box and the dollar stores. Space ships often have electrical cabinets you could slice and dice. The very bottom of the box is home of the cast off items. Usually interesting at least as kids will save a cool cast off too
Sheet metal, in plastic like a q-tip box or thin metal flashing. Just a few on a pallet or leaning against something, It might bow
A board walk or mud sled /bridge over the ever present huge puddle that nearly every yard has.
A boot, or new tennis shoe stuck in the mud nearby would be funny .
A RR executive with a lost dress shoe would be funnier.
Anyone make an "oops I stepped in doody" figure? It would be the right pose.