We spent 5 months in the Australian deserts as a series of separate entities, always trying to find each other. We used 'Skystreme' emergency kites, which are brilliant. Designed to stay afloat in almost no wind. Self launching after no wind, incredibly strong and designed to give off the radar reflection of a small aircraft (for search and rescue radar). As it happens, they weigh nothing, and when packed are smaller than a packet of cigarettes! They've won all sorts of awards...
if that's not product endorsement, I don't know what is!!!!!!!!
I think you can get them in the better outdoors shops (or try an internet search)