A mini / small rain poncho should be have maximum 1x1 or 1x2 size.
It is like a mini poncho, you can place it in your pocket. It is water-resistence, but can be damaged realy easy by one (zombie) hit.
It should have three colors: transparent, yellow and maybe green/camouflage.
Maybe a secend military poncho with camouflage which is little more resistend (2-3 hits) as the normal poncho.
The ponchos should be worn on all clothes (over the torso and a peace of pants).