Tiny lengths of fat metal rod or slices of the Right gauge of hypodermic needle for tins, then model  oil cans from oblong of strip wood decal led with microscale decals from a gas station set. My HOscale set includes a decal for stacks of Shell gallon oil cans.  When modelling a scrap metal load for a gondola remaber the source of the metal effects the load. Loads from a automobile factory will be mainly scraps of bright steel sheet. Loads from a demolished industrial structure will be girders, ladders, wheels etc. Acarefull y dismantled structure might have scrap girders loaded on a flat car.