Polycryo-teltunderlag

Used it as a ground cloth under my tent on a wet weekend and the floor stayed completely dry. It's thin enough to fold into a pocket but didn't tear on rocky ground.

This thing weighs basically nothing in my pack but saved my tent floor from a week of pine needles and grit. The polycryo crinkles a bit when you first unfold it, though it flattened out fine after the first night. For the price and the weight, I'm keeping one in every pack.

Used this under my tent on a rocky trip and the floor came home spotless, no scuffs at all. It's basically a sheet of plastic, so it crinkles a bit when you unroll it, but it folds down tiny and costs almost nothing in weight.