Working in combinations materials in "Mixed Media" is fascinating. Of course, by definition, it can also mean almost "anything" since it's a way of working that leaves the door open to the artist to freely combine materials, images, shapes, and techniques as inspiration dictates, for both "flat" or textural "dimensional" results that can even become almost sculptural.
Among the materials I enjoy using are pastels, acrylics, metallic substances, inks, pencils and colored pencils, photographs, wax materials, and even introducing some digital aspects. At times this type of work will also develop into a collage including other materials completely. It's an open field, so to speak, and a very exciting one.
For example... Starting with pastel, working with it in collage, layering color and materials with Venetian Plaster followed by more pastel, some shapes in 3 dimensions...and finally paint and pencil. Meanwhile, a lot of physical working the surface. Here's a mini-video (silent, again...) showing the steps as they occurred in development.