I keep a backpack in my car with at least two changes of clothes, allergy pills, ibuprofen, sunscreen, and deodorant, toothbrush, and first aid. Worst case I'm ready when shit hits the fan. Best case I'm always ready for a surprise slumber party.
I just like to be prepared for if I get stranded during a storm or my car breaks down
You'd want to leave a little space in the containers so they don't burst if they freeze. I think it's still worth having at least some emergency water even if you might have to figure out thawing it.