So as you as you can see, for our base material I used dry split peas. I used such a big bin that it didn't cover the entire area though, so I also added some green aquarium gems. These are one of my daughters favorite base materials. Some things I added to the bin were a plastic ring, plastic egg, pom poms, bead necklaces, paint swatch sample, my little pony, magnetic letters, PINK dog, turtle bath squirter, little people tractor, and measuring spoon. All green of course. Your items may vary, but as long as they're green that's what matters.
My daughter loved this bin and dug in!