The California Sunbounce Sun Swatter Big 2/3 Kit is a great way to reduce light to more manageable levels on-location.
The kit consists of an easily assembled aluminium frame which supports a 180 x 245 cm (6 x 8 foot) 2/3 stop diffuser screen, plus a carry-bag.
The frame can be held in place by hand or a grip head, reducing light levels or creating areas of shadow.