I have a mate in the US that is mega into this prepping since hitting civvy street.
We've had many a chat over it as his tactic is to store as many guns and ammo as legally allowed.
He stocks up on rice, wheat, bleach etc etc.
My opinion is that if the S does HTF big style then the ONLY way you'll survive long term is in a social group.
He is currently recovering from glandular fever which has had him on his back for pretty much 2 weeks, last year he broke his leg motorcrossing.
I explained that if he was not in a group then there is a good chance either of those would have eventually been fatal.
Odd thing from me as a Brit is that talking to Mrs parents (Greek) when they were kids they grew up in villages that had no electricity, no roads and were pretty much closed off to the rest of the world 4 months a year.
Her Mum can go out up the mountain opposite and come back with a half decent meal we eat fresh χόρτα at least once a week.
As a keen fisherman i'm confident i can supply food most days, me Jack Russell although not trained to catch rabbits wouldn't need much training after not eating for 2 days i guess (if no fish were caught).
I know of 2 fresh water wells in the area, so that's sorted.
The guy opposite is a carpenter so it'd do well to get in with him
I think wandering mobs aside we'd be ok for a few years, problem then would be things like antibiotics, tinned food running out, bleach, lack of wood (well Athens has 6 million people and only a very small wooded area, it wouldn't take long before all the trees i'd be gone.
With no bleach and no wood we'd then struggle to render our water supply safe.
Oddly enough if the **** then it's bleach i'd stock up on first.
Boats are a fail IMO.
Sail boats aren't big enough to give a consistent supply of food
Motor boats consume fuel at a rate unimaginable.
For the massive boats being discussed your talking at least 1000 gallons per hour being burned.
The engines alone having a displacement around 25,000cc
Being 2 stroke turbo diesel engines they are massively efficient, but still your slow, big and a huge target as fuel is going to be VERY precious.
Even on small boats, if i'm REALLY careful i can get 15 gph out of my boat (that doesn't leak

).
For sure that's no where near big enough to grow food on or raise lifestock, after a weekend on that you've really had enough, never mind live aboard.
Cheers
Mark