This is one of my favourite fallback lessons which I have been doing on and off for the past few years. I'm not sure where this idea originally came from, so if anyone knows, let me know!
Students begin by dripping watercolour paint in a random pattern on their paper.
They then choose about 4 different coloured textas. (I usually ask them to choose either a warm or cool colour scheme).
Using one colour, they must trace a contour line around each drop. Then they use the next colour to trace and so on, repeating the pattern until they reach the end of the page.
To me, they always look Aboriginal inspired, like aerial desert landscapes or water.
You could use this lesson to teach about Aboriginal art, colour families, pattern and contour line.