When I was ordering waterproof zippers for my pack from Ripstop By The Roll, I threw in a couple rain poncho kits, too. Doc has a rain shell but I don’t, but I was also thinking about coverage for our legs and packs. Ponchos were the answer.
I finished mine first since I still had orange thread in the machine from my pack. The kit had all the hardware and pre-cut fabric so it was a fast sew. It even includes a rectangle to make a stuff sack for it!
The instructions say you can add tie loops to the hem to use this as a ground sheet or tarp in a pinch. (Prepared for every eventuality? YES.) I skipped hemming the sides since the fabric was silicon-impregnated and didn’t seem like it was going to fray, but added two KAM snaps on the sides under the arms and used grosgrain tie loops as the snap reinforcements. 
I’ll get Doc’s sewn up next and then we’ll have two ponchos, or one ground sheet to sit on and one tarp to keep the rain off. JUST IN CASE.