One interesting exercise I did in my AP art class was to draw with charcoal and a white chalk pastel over acrylic paint.
Essentially, what we did first was take a few colors of paint. Complementary colors (colors opposite on the color wheel, red/green, purple/yellow, blue/orange) work really nicely. Then go Kindergarten on a big piece of paper/drawing board…something papery as opposed to canvasy so that the paint can soak in. Mix one of the colors of paint with a little water so that it will soak in better. Wait for it to dry. Add more colors, and these ones can be thicker in places.
Then what you want to do is wait for it to dry completely. I had to wait overnight on this one because the red was so thick it was three-dimensional and the green was so thinned out with water that it wouldn’t dry quickly. Afterward, take chalk pastel and charcoal–I chose to make mine black and white but I suppose you could go for any colors–and draw your image over it. The chalk will have a harder time going over the thick, plasticky areas but appear clearly on the thinned-out part, giving a cool effect that you can see.
A lot of the other people in the class made beautiful pieces from this exercise…I wish I had copies. One in particular was a dark canvas with some red streaks and a big, red handprint in the middle, which the student then added some figures to make it into a piece representing the holocaust, if I recall correctly. Obviously you don’t have to make this sinister, though. Lighter colors in blue and yellow could become somebody dancing in the rain, or a kind of abstract scene. You could use this to spice up and add some color to a still life. Etc, etc, etc, etc.