We're very happy with our "Warmlite" (Stephensons Warmlite) ponchos. They cover our backpacks and length is adjustable for when not wearing a pack. Material is Silicone infused ripstop nylon. When we ordered ours one could specify custom lengths and colors, even having each panel (including the 3 panels in hood) a different color - check with them if interested in this.
We also made waterproof leg sleeves (chaps) of the same material, purchased from Warmlite (or elsewhere). Each leg is separate, cut at a bevel at the top and fastened to belt loops with shoelace strings. We made them large enough to fit over boots and provide ventilation (and vapor) proof.