Regarding potassium. If we check the mineral content of all food, we find that literally ALL food contains very high amounts of potassium(and phosphorus), both from the animal and plant kingdom.
The soil is heavily replenished with potassium, nitrogen and phosphorus.
What food lacks is sodium, chloride and calcium.
High calcium is found only in raw milk, raw cheese, eggshells, sesame seeds, fish bone.
Sodium and chloride is salt. I guess thats why old timers salted everything, to balance out the high potassium contents of all food groups.
Phosphorus needs to be balanced with calcium. I guess thats why milk/kefir/cheese was added to almost everything, to bring up the calcium in a meal. Adequate intake of calcium and phosphorus in the appropriate ratio of 1–2:1 (Ca:P)