Maybe carry a 5x7 white/grey card or even a little fold out white reflector ? they are also great for setting accurate WB
I think everyone is missing the point towards Run N Gun - Observational documentary. When filming this we really can only rely on skin tones, as following someone indoors to outdoors in unexpected scenarios.
I would never carry a white/grey card and put it in the scene to break it up and say "wait i just need to get my exposure".