I usually carry a US GI woodland camo poncho along with an Adventure Medical ThermoLite Single Bivy (8 oz) in my daypack. Between the two, I would be able to create a snug three-season bivouac. Also, when backpacking I carry an Adventure Medical Kits Mylar Emergency Sleeping Bag (2.5 oz), just in case something happens to my down bag. While Southern California is not known for its many mountain ranges, they tend to be very rugged. Several times a year there are stories in the news of lost or injured hikes being stranded for a night or two before our excellent EMS services can locate and extract the errant hiker. Therefore, in answer to your question carrying a poncho and Bivy Bag of some sort are not over overkill in the least. My day hiking and backpacking kit are always together and serve as the basis for my earthquake disaster supplies.