Gouache paintings & charcoal drawings
Both of these media are so efficient and quick to work with. A small drawing or painting can take as little as one hour. They are also both very forgiving. Gouache can be painted over, since the pigments are opaque, unlike its transparent (and unforgiving of errors cousin, watercolour). And charcoal is so malleable...you can darken it using pressure, and then pull out light areas with an eraser. It's all about pushing and pulling until you get where you want to be.
Paula Banks