In Joy Thomas's
The Art of Portrait Drawing, it is made very clear that having the right materials leads to a successfully drawn portrait, "It's challenging enough to create art without having to fight inadequate materials." Not having useful materials causes drawing to be challenging, especially drawing realistic portraits because there are so many aspects of the human face that you have to capture that can't be easily achieved by using one of your average go-to pencils.

One of the materials that may be very useful while drawing is
charcoal. Between vine and willow (two popular types of charcoal to use for drawing), willow will probably be the best choice because it has the best consistency, easy to manipulate or remove, and is used in preliminary work. It comes in many different varieties of shapes, textures, and sizes too! It's velvety dark mark is used for making broad stokes in your portrait, which makes it very easy to create large portraits if you wish to do so.
Other materials that may come in handy are
subtractive tools. Although subtractive drawing may be mostly known as a beautified phrase for erasing, but there's more to it than that-it's about lifting the tone of the picture to shape form, adding a line-texture, or creating highlights to give a more three-dimensional look to your portrait. Retractable erasers, kneaded erasers, gum erasers, extra-soft erasers, single-edged razor blades, and bristle brushes are all counted as subtractive tools.
A few materials people may not know much about because of their goofy names are
tortillions, stumps, and chamois cloths. These tools are a must for toning your portraits!
Lastly,
graphite pencils, ink, and silverpoints are essential for creating a portrait. Graphite has been used for drawings for centuries! It comes in many different forms as well. Graphite pencils today are formed from a paste mixture of graphite, clay and water which after that, is fired. Inks are available in a whole spectrum of colors. Traditional favorite inks include the transparent and luminous brown-bistre and sepia. Ink drawings vary according to the tools and techniques used while forming a portrait. Silverpoints consist of a sharpened silver wire held by a stylus and is known for making precise marks.
Although having proper materials can be very helpful for drawing or sketching, do you think someone needs these many materials for one portrait? What are your thoughts on constantly replacing these items as soon as they are worn out?
Thomas, Joy.
The Art of Portrait Drawing: Learn the Essentials Techniques of the Masters. New York: F+W Media, 2012. Print.