I bought a reflector! It's a portable fabric circle, which stretches out and collapses like a half a car windshield shade. It has a cover, 2 circular sheets sewn together like a pillowcase, with a zip at the opening. There are 4 sides to it: white, gold, silver and black, different reflective (and one absorptive) surface for different purposes. I used white in this case.
I knew I needed a reflector, as I was going to taken an outdoor afternoon photo to in front of the golden gate bridge. He's holding the reflector to the right, reflecting sun light into his face; you can see how his chin is lit up, but not so much as to take away the form of the face. The reflected light is creating what's called a "fill light" - ie, filling in the shadows. Otherwise, the shadows would be very harsh, and features obscured. It looks more natural than a flash, but a flash could also work as a fill light. Yes, it was a beautiful day in San Francisco!