I overheard this idea somewhere today that would be fun to have the kids do in class. The suggestion was that students measure the thickness of their math book to provide slope for an equation. So based on that, the students can measure a stack of two, three, four books to identify the pattern. Then they take the information to create a graph and write the slope of a line. If you want the line to start at a y intercept other than zero, you can start the pile on a footstool, a chair or a table. Then you have the students use a different set of books such as a classroom set of goosebumps again on the floor, a stepstool, etc. This can be repeated with several different books.
I just found out that quadratics are used to calculate vertical curves on the highway, roller coasters, etc. If I remember correctly, there is a free video or two on itunes university that help show how the math is used in building roller coasters. That would make a nice cross unit involving both math and science. That would be cool to include the mathematical equations for the roller coasters.