Lots of birdseed gets moved around here to the various feeders though sadly none of it takes the same route as the railway. But as an experiment in simply carrying something real this operation did work rather well.
Later on, as the railway expanded (it’s now about twice as long) a more practical job emerged. Basically, moles make their little hills at one end of the layout and I store earth about 250ft away, quite near the other end. Running the train merry-go-round (i.e. not down any sidings) gets the job done. It’s good if I’m chilled out and in no rush, because if there’s a lot to shift the wheelbarrow is of course hugely quicker. Let’s say that railfreight here has reached the stage where it’s now verging on being almost useful !