In 2007 this area experienced serious flooding, in fact our street looked just like the one in Andy.H's picture.
I know a lot of places were hit badly by the floods that year, but we were forgotton. No news teams came, no "Got to help these folk" messages.
Not too far from where I live there were houses with flood water going into upstairs windows, it really was that bad.
We lost a lot, photographs etc were destroyed and the electronic backups were on the computer that got fried (not by the flood itself but simply by the humidity generated by so much water in one place).
This taught us a lot and I'll share it for those in a flood area considered at risk.
1) Put ALL photos and mementos into a sealable box, those clear plastic ones you were looking at in Wilko's wondering if they would work as a HLT would be perfect. Make sure your insurance documents and ID are in there too.
2) Find the water stopcock, electricity main breaker and gas shutoff valve. Make sure they are accessable, trying to do this with water round your ankles isn't fun.
3) Emergency services WILL be overwhelmed with calls for help, Vulnerable folk will be seen to first - I'm sure you would want it that way, just a reminder.
4) When the power goes out it isn't the end of the world, it only feels like it. Camping stoves still work as do torches etc. just remember to take fire precautions.
5) YOU CAN'T SAVE EVERYTHING! Life is more important than things, make sure you and yours are safe, then check on neighbours. Old Mrs Fidget at number 23 might need help up the stairs, especially if she's panicing.
6) A battery powered radio can mean the difference between "what's happening" and "It'll be alright" - Knowledge is power, in this case the power over fear.
7) If the water gets in it's bad news. If the water doesn't, it could still be bad news. - Water can affect the foundations, make sure you get it checked out by the insurance people afterwards.
I'm sure others can add to this because I know I'm not the only one to have been knee deep in water.