Painting is always nice, and painting on other surfaces besides paper and canvas is nice also. All you need is some nice smooth rock or wood and voila you have a painting surface. What is wonderful about painting rocks and wood pieces is that sometimes the shapes are made for you, you paint what you see.
I too have dabbled with painting rocks when I was younger and again recently while painting with some kids. Painting rocks, if fun and fairly cheap if you have rocks around, and paint already.