1. Styrofoam head.
(Many different websites sell these, but the cheapest I found were at www.valuedisplay.com )
2. Flesh colored spray paint.
(They don't actually make a "fleshtone" spray paint, so just get the one that looks closest to your actor's skin tone.)
3. Make-up kit
(Don't you people get it yet? Buy a simple make-up kit with some different flesh tones and reds.)
4. A wig.
(The foam heads come bald, So unless your actor is bald you'll need a wig.)
5. Glasses, mustaches, etc.
(Distinctive items like this that can be worn by both your actor and dummy head will help to fool the viewer.)
6. Fake blood.
(No matter which way you end up "offing" this poor dummy head. You'll probably want some fake blood on hand. Mix Corn syrup, red food coloring and a splash of chocolate syrup for yummy blood.)
7. Liquid Latex.
(To add some "fleshyness" to the face.)