Depends on the actual scene and the lighting. If the person is front-lighted or mostly side-lit by the sky, then no worries, easy. if the person is back-lighted, and their face is in shadow, then reflector fill is the easiest weay to get their face exposed well; the reflector can be a photo reflector, a white bedsheet, a large section of sidealk or concrete, beach sand, or a large building or car that reflects light. Working close to buildings is a great way to get shadow fill-in and thus bring the exposure for the sky closer to the person's expoisure level.
A second way is to use Shadow Fill-in controls in software! Digital Fill Light was introduced in the early to mid 2000's, as a software method that was/still is incredibly useful! At one time, we had to individually mask such areas, but nowadays "fill light"sliders allow pretty amazing fill-in on darker areas.
But, for no-flash fill-in lighting, I think that reflector fill is the easiest and best method for on-scene lighting adjustment. And again...consider that a large building can provide a huge amount of shadow fill-in lighting!