I can see being able to keep perishables cold / frozen by putting them outside in the winter, but how do you keep stuff from going bad in the summer without a refrigerator or freezer?
Here in SE Alaska the water temperature is a constant 40 degrees. Nice and cool in a locker below the waterline. Similarly in NW Washington, during Winter of course, the freezer is just a milk crate outside in the cockpit.
Hawaii required different tactics; An ice box for the beer and more frequent shopping.
The passage between the mainland and the islands can run well over a month in our boat. That is more of a challenge for the First Mate/Galley slave, Freeper Patriotic Rose. She manages to have fresh veggies out to two weeks at sea and things like onions, acorn squash and yams over a month. Supplement with cans and freeze dried stuff. Wouldn't want to go much over 8 weeks (But we could. MUCH over 8 weeks).
The techniques are well known to Old School cruising sailors. We are not exactly "Preppers" unless you consider being prepared to be out of sight of land for a couple of months and doing it several times.
All I know is canning or dehydrating are good alternatives.