Most of us have since lost our ability to sit cross-legged for hours on end in the years between elementary school and now, which means sitting on the ground is extremely painful. But what if you have no other option? Here's a weird DIY strap chair that will help a little.
Instructables user higginbo uses a long strip of tubular nylon webbing, but recommends nylon or any other long, flat materials -- even a seat belt -- that's light enough to be throw into a bag. When done, you'll have a strip that hooks around your legs and back and provides a bit more support.
Of course, you'll look like a doofus with a belt wrapped around him, but old people like us can't complain.
Seatless strap chair [Instructibles]