This being the era of the exoskeleton, today’s invention is an ultra-simple, unpowered version that acts purely as a seat.
For older people, who can get around but enjoy a short sit down on occasions, carrying a camp seat can be a pain and a shooting stick isn’t much use on smooth surfaces.
Enter the lightweight exopants shown. These consist of a double-hinged shell for each leg (probably held up by being clipped to a waist belt). When the wearer wants a rest, the act of adopting a sitting position causes the edges of the hinged sections to contact each other and form a stable, weight-bearing temporary structure.