We did a lab tour one year that was great; they were given a sheet with questions for each part of the lab (so they would interact with the staff). If they filled in the correct answers they received a small bag of candy at the end. For Blood Bank it was "what is the most common blood type", etc. We also had an educational station for each department. After explaining how we read tubes to determine blood type, we showed them one and they had to figure out what the blood type was. In Hemo, they had slides of various diseases to show them (sickle cell, leukemia). In Chem, a demo of our automation and a big poster explaining how hemolysis, clotted samples, lipemia affect results. In Micro, they had a display called "the colors of Micro" with plates showing different organisms that are colored. We had a great turnout, many said that they had no idea what we do in the Lab. Our CEO loved it.
Other fun things: decorate a cookie contest (decorated like white cells, red cells, micro plates, and yes...even a C diff cookie...ewww). Decorate lab coat contest.
And of course food. Way too much food.