Drawing on a paper cup in an airplane
drawing on empty pistachio shells (I have a bag full of them... shells, not pistachios)
a duracell battery
iron supplement tablets pack
camera lens cap.
These days, the moment I hold a pen or pencil in my hand, I have an uncontrollable urge to draw on whatever surface is handy, including my mac and my own body.
Some might say that I have no plain sheets of paper to draw on...