For everyday carry in a smaller kit, I carry both a large HD trash and leaf bag and a space blanket or emergency sleeping bag, depending on the kit I have with me. I fold the trashbag around the emergency blanket/bag and rubber band them so they form a very compact shelter pack. But then, it regularly approaches or dips below freezing at night during winter and even mild nights are generally in the low 40s so I feel both are necessary. If my conditions didn't warrant both, I'd drop the garbage bag and keep the space blanket which is a more versatile piece of equipment in my opinion. For my BOB, I'm looking into getting military issue poncho w/liner.