I remember getting soaked in the Sierras on a backpack trip wearing jeans back in the day when synthetics were for discos and not the outdoors. Luckily we had Gary H., a pyrotechnic along, expert at starting fires who also carried a clean t-shirt for every day of the 10 day trip. After the storm, my friend and I snapped our two army surplus rain ponchos together and pitched a tent. Not exactly a bivvy - I have yet to have my first.