Best to avoid the wind by shooting either very early in the day or very late in the day. I calculated that even with a 30" reflector in 18 knots of wind - and it only takes one gust of that velocity, that I would need about 70 lbs. of sand or water, hardly a portable setup. Yes you could use bungee cords and tent stakes but that is a pretty inflexible setup and not viable in many locations if the surface is too hard or you are on public property where pounding stakes into the ground is frowned upon. An alternative in some locations is to use flash and bounce light off a rock or wall or car that serves as a reflector. You end up with a much larger light source by virtue of the bounced flash. It works better than you might think.