The painting you see below is one that was started from the excess paint in my tray.  In between working on my other paintings.  I use one or two canvases to use up my leftover paint from my main paintings.  The beauty of this is two fold, one I recycle most of my paint and two it allows me to be totally free on the subject matter.  That is until I start to pull things out of the painting and then well its time to start another excess painting.