I'm a hammock camper so I don't have a ground sheet. In an emergency I realized I can use my map as a ground sheet for my torso. The I can use my pack for my feet and my rain jacket for my head.
I'll have a "torso" pad (though it's a bit small for that) that I use for my feet that I can use under my back.
I would be a BIT cold but this is only plan B in emergencies. For example, getting stuck high in the mountains without trees when a storm hits and having to sleep through it.

