I've had some success with a DIY solar oven. All you need is:
1. A dutch oven, or camps stove with a lid.
2. An oven safe nylon baking bag (Reynolds makes em.)
3. One of those silver, reflective car windshield shades.
4. A couple inches of adhesive backed velcro.
Basically, attach some of the velcro to the top edge of the windshield shade to make it into shape that reflects light to a central point (a bowl, the corner of a cube, or a simple V shape.) Fill your stove with whatever goodies you'd like to cook, then place it in the baking bag, and place the baking bag in the center of the reflector. On a really bright sunny day, you could ideally bring the temperature of the stove up to 350* in about 15-20 minutes so you can pretty much cook anything you feel in it. Have fun!
More detailed instructions at http://solarcooking.wikia.com/wiki/Windshield_Shade_Solar_Cooker