Since I'm almost always in an area with plenty of natural shelter (overhangs, etc), or at least shelter-building materials, I often carry only a contractor size trash bag as an emergency shelter on day hikes. I carry a smaller trash bag for sitting/kneeling when taking photos.

In colder or constantly rainy weather, I might add one or more of these:

• lightweight vinyl poncho
• breathable nylon rain pants
• PVC rain jacket (for constant cold, wet weather) (I may replace this with a breathable rain jacket.)

I'm always dressed in synthetics, usually have at least a fleece jacket, hat, and polypropylene glove liners. I often just leave any raingear packed and enjoy the wet hike, even down into the 30's.