Reflector - Big Triangle
The classic cycler's triangle from the '70s, and although we've described it as "perfect" before, but now it really is, because we (well, I/Grant) take them out of the plastic and add a 7-or so inch length of elastic to the belt, so good god you can have a 35-inch waist and not max it out anymore. It should go up to 42 or so now. I modified it crudely but effectively, and if you can't deal with that, don't buy it—but I've made it better for wearing over winter clothing. We're eliminating the packaging.
It shouts to approaching motorists, and works nearly equally well day or night, where it's 99 percent as effective as a light. The whole yellow-orange combo works way better in daytime than a tiny blinking light, too; and it's a reasonable alternative to neon green windbreakers.
Attaches around your waist with a 3/4-inch belt closed with a quick-release buckle.
Is she visible? Pedal-reflectors, Scotchlite tape, big triangle.
Is this visible? Wrappit around your laptop case/messenger bag.