I'm lucky I still have a heavy military rubber poncho. Which I have used as a lean-to recently. I don't carry in my BOB as the heat here in the SW would rot it out pretty quick over a summer in my trunk.

I am not a big fan of ponchos. waterproof gear and tents are light enough now that I don't find them necessary. I've tried some of the Frog Tog waterproof tops and bottoms and they work great, except they can tear rather easy on the butt and knees, but the stuff is made for duct tape. I went with a size up on the top and I wore my REI Mars pack under the jacket in a rainstorm and it did great. The are very oversized tops