A fast moving/rising flood situation it's easy to become separated from a kit that's not on you. Carrying a small kit at all times would be wise. At best all will go well and neither kit will be needed. At worst you'll have just the kit on your back to make it through a wet cold night.

I already have an EDC backpack. Lotsa stuff in there that would be good. It doubles as my gym back and is the bag riding in the truck to carry odds and ends that don't carry well in pockets. Some of the contents change with the season and some with my daily activity. Water is always fresh, bottle is refilled just before I leave each day.

Tailoring the backpack for a flood situation would be a no-brainer. Haven't thought about the specifics of what I'd add, but then I don't live in TN. . .