

for days minimum
This will be up to two relevant factors, only the first you know in advance:
- The more densily populated an area the more effort will be spend locating survivors, if you survive a flood but live remotely it on average will take longer before you are located.
- The extent of the emergency, the bigger the area the more available resources (including effort/ human energy) are spread out. If the flood covers a lot of area, it will on average take longer for help to reach you.
It is very unlikely there will not be any help coming.
If you survive a flood you might have gotten wet which will have massive influence on your ability to maintain a desirable body temperature. If the flood comes with bad weather and you have no acces to heating or a place to shelter hypothermia might kill you before contaminated water can. If you can shelter in place and you’re safe in your own (or somebody elses) home bottled water and/or a water filter might be a great thing though, just trying to say what you’ll need depends entirely on what situation you end up in.
This one only goes for people who trust their government or an ngo to come rescue them when there’s an disaster or other emergency going on. I am one of those people, but there seems to be a lot of people who don’t and want to buy stuff now they can so they can survive as long as they can without any help when the point comes they can’t buy these things.