Homemade cake balls:

At school, our Student Council gave baggies of Jolly Ranchers to all of the staff:
~Mrs. Scott
This would make a great classroom lesson for lower grade levels (4-7th). I bought some gumdrops from Walmart (mini marshmallows work too, but aren't as colorful), and used left over spaghetti noodles and toothpicks.
Students build 3-dimensional shapes (could work with 2-d shapes too) using the supplies given. We built cubes, triangular prisms & pyramids, rectangular prisms & pyramids, and then students calculated the number of faces, edges, and vertices, and showed me which side they would use to calculate "B," the area of the base.