Given a box full of some uniform object (paper clips, bb's, drinking straws,
etc.). Find the mass of one object without counting. Slowly dropping paper
clips onto as scale (tink, tink, tink) is counting. This models some of the
thinking behind Millikan's oil drop experiment.
Another one I use that is full of things for my students to think about.
Given the specific heat of water and a good calorimeter, find the heat of
fusion and the heat of vaporization of ice.