I keep a couple of clean dry socks and thin plastic bags in my trunk at all times. If my feet and shoes get wet, I can at least put dry socks on, and the thin bags, slipped inside of my shoes will at least keep them dry. I also keep in the trunk a plastic coffee can as a pee or in desperation a poo container. In that can I keep a change of underwear, some TP, wipes, and sanitizer. During the winter months I add a long handled shovel, tow rope, and sleeping blanket.
Years ago, hundreds of people got stuck on the NY Thruway over night due to snow. If that ever happens to me, I want to be prepared.