Tip of the Day: If you ever forget to bring your sketchbook, improvise i.e. a Beef Patty Bag.
What if you don't have a pen or pencil?
You don't want me to answer that lol.
Any liquids and some newspaper to make a watercolor? Maybe pick up a stick in the street and some dirt, mix it with water, lol. Anything is possible. You also always have your blood. D: