If I recall correctly, caraway seeds is what Irc Schultz used on his layout, he had lots of pickle cars and facilities. It’s definitely mentiooned in the April 1990 MR, page 89, where is packing plan was Model of the Month.
If you are prone to mice in the layout room think twice about seeds.
Another food product that might work are the candy sprinkles or “jimmies” that people put on cakes and cupcakes. Some even come in green. Of course the same critters that enjoy seeds might feast on the jimmies as well.
Tiny bits of green florist wire are another possibility and I am not aware of any animal that eats them! Green putty (squadron) rolled small and cut into lengths, or green PlayDough might work.