Credit wushuair/Instructables
Baking cookies on your dashboard is one way to use the sun for cooking, but for a more versatile--and portable--solar oven, check out this $6 version from Instructables. Cardboard boxes, aluminum foil, and sheet of glass let you turn out pizza, muffins, or even cookies (without that hot-car taste).
You'll be able to find most of the materials in your garage: two sizes of cardboard boxes, scrap paper, black spray paint, duct tape, aluminum foil, and a glass panel (the Instructables user who developed this project had to buy a sheet of glass, which is what took the price from $0 to $6)--plus an X-acto knife, scissors, paper shredder, bricks or canned food, and a food thermometer (to make sure your finished product is safe for eating). The basic idea is simple: Surround the smaller box with shredded paper so that it fits into the bigger box; paint the smaller box black to catch more of the sun's radiation; cover the flaps of the larger box with aluminum foil; then lay the glass on top to keep the pressure (and temperature) even.
While this is a fun backyard science project for kids on summer vacation--try making your oven in the morning and then cooking lunch in the finished product--a modified version could also work for short trips or camping weekends (my mother-in-law is famous for using a similar cooker 20 years ago to make muffins at campsites in the middle of nowhere).
