There's the famous Afghan skin bag: cut the skin around the belly, pull it over the head of the victim and tie it like a bag ; then let the victim bake in the sun and slowly die of exposure, while being half-asphyxiated inside their own skin. Oh, of course the victim will try not to fall on the ground for a while, where dust, ants and insect will exacerbate their suffering. IIRC you can agonize this way a couple of days before dying of thirst.