You know your situation better than I do so this is as much a question as a suggestion; even though you're on a hill where you won't be personally flooded, couldn't a local flood disrupt normal services to your home? Elect.? Water/sewer? Availability of groceries? Etc.?
We do get floods here, usually the first heavy rain after the summer is pretty bad as inevitably all the drains are blocked with rubbish that's piled up all summer.
In Athens though it's unlikely there will be a flood severe enough to dramatically affect food supply.
For water i have around 800 litres of fresh water in my various tropical fish tanks.
As above i wouldn't to drink it straight out of the tanks, but i have filters, purification tablets, bleach and equipment to boil the water in, so i'm confident we have enough water for a few days if needs must.
Electricity supply is very inconsistent here, but to be honest that's a good thing as it means you don't depend on it and have alternatives.
I have a small generator for essentials like the freezer, we have a fire place with plenty of wood to keep us warm in winter (doesn't tend to get THAT cold here anyways).
It worse when we get power cuts in summer, as mid 30c's to mid 40c's is not exactly the most comfortable of sleeping environments.
It's not really much more than a inconvenience though.
Sewage over flowing would have to be pretty bad as we are on the 4th floor at the top of a hill, and as i remember the saying poop runs downhill
If food supply becomes a problem though then i'll grab my fishing stuff, set a few traps at the mountain and teach the dog how to catch rabbits.