STEM Bins: Hands-on Solutions for Early Finishers.  STEM Bins are plastic school boxes filled with an engineering manipulative of your choice, such as Legos, pattern blocks, base ten blocks, unifix cubes, toothpicks and playdough, or popsicle sticks with velcro on the ends.  The boxes also contain small sets of task cards on metal rings that picture a variety of basic engineering structures.