This two-page worksheet teaches dimensional analysis and unit conversion, and is the perfect cure for a class that complains units don't matter. Air Canada Flight 143 ran out of fuel in midair because the flight engineer miscalculated how much jet fuel he had and the fuel gage was broken. This true story includes 9 calculations. The first is done for the student, and the second two are scaffolded.
This two-page resource is a bit long, but could make a nice activity for a substitute, or you could just use the first page. For something shorter, with less reading, I recommend Ichy Math.