Some of our best resources for impressive experiments and activities have come from our science teachers and the Internet. More than anything I would like to impress upon you that the activity must be FUN! It cannot resemble book work or schoolwork.
Our “Structural Engineering” meeting we supplied each group with a bag of mini marshmallows, 200 toothpicks and a strip of blue paper-4 inches by 12 inches (“the water”). The challenge was to build a bridge out of the toothpicks and marshmallows. The bridge could have no more than 2 points of contact with the water.

Our “Chemistry” meeting we made elephant toothpaste. This can be a very impressive demonstration of an exothermic reaction. You will need the supervision of a science teacher and she will need to order some Hydrogen Peroxide ( preferably 30%). This cannot be purchased by the public. She must have teaching credentials to order. In a pinch you can buy developer from a beauty supply store. It is only 6 % and does produce a not quite as impressive a reaction. One of our high school teachers let us make up a solution of Potassium Iodide. You will also need a little dish soap and perhaps some matches.
Blue solution
During the “Mathematics” session we are making and shooting foam rockets off at different angles and measuring the distances travelled. This activity and directions can be found on NASA’s website, http://www.jpl.nasa.gov/education/foamrocket/. This activity could just as easily be used for a “Physics” session.
We are scheduling a 2 hour coding party for our “Computer Programming” session.
During an “Earth Science” or “Geology” session you can create layers of sugar, cocoa, nerds candy, crumbled cake, frosting in clear drinking cups. Use transparent straws to take a “core sample” so you can analyze your sample. If you layer each cup in different order then you can compare different samples. http://www.womeninmining.org/activities/Cake_Core_Drilling.pdf
Overall any STEM topic you find a speaker for, you can use the Internet to search for a related activity