I spend way too much $$$ on photography so I'm always looking out for ways to save money. Rather than buy a fancy, and expensive reflector set, I use white foamcore boards. They work really well, and at $4 a sheet it's cheaper than the cheapest reflector. Poster board and mat board work just as well; I like the durability and stiffness of the foamcore. Sometimes I wrap it in aluminum foil for more specular lighting. I carry a couple of spring clamps so I can clamp several pieces together to make one big reflector, or clamp the foamcore in position, etc...
Not that fill flash is all that complicated, but using reflectors is just easy, and works well in most portraits.