Natural loose parts are by far the easiest to come by and most beautiful (in my opinion). The seasonal variety is amazing. They can cost very little if you are a good hunter. Colors, shapes and patterns are endless. They are also less precious so if something gets broken, ends up in a pocket, or moves into an art project that is ok (maybe even encouraged).
Here are some of my favorite arrangements and presentations of natural loose parts. Any of these can be done in your playscape. We often offer a loose parts table to help organize the activity near the loose parts storage area. The following are arranged in a sand box, on a black piece of fabric, on a wood top table, in pea gravel, in a small wooden grid, and in a wood box with small compartments.
You may notice all of the arrangements are quite beautiful. Kids respond to this and the organization and beauty of the materials will inspire even the littlest hands.