How about a mixture of ground weeties and corn flakes for ballast, spaghetti for power poles and logs, rice and rice bubbles for water-warn boulders, flour for snow, Gravox for a dirt road, jelly (jello) for water, and a cat to control the rodents?
A friend of mine had an entire mountain forest on his layout made of actual weed twigs. It was very impressive looking.
Then one day he noticed his forest suddenly looked rather logged-out. And then he noticed the tell tale signs of the mouse digestive process all over his layout … He had no cat but his two big dogs seemed uninterested in coming down to the layout room. He set traps and killed dozens upon dozens of mice.
I recall one article in the old-school RMC a number of years ago, where the author created building demolition debris using uncooked lasanga noodles, smashed into small pieces, for a building demolition diorama. I believe he painted the pieces and gave them an protecctive overspray to prevent any insect infestation. I’m fairly sure it wasn’t an April’s fool article, as the results did look pretty decent.