Foods that people canned themselves and then they fermented or aged. Things like sauerkraut, pickles, canned fruits that may have became a little tangy, canned vegetables.

They can't be things that the stores can because those are pasteurized, boiled, pressured, or whatever to make sure they last a long time without changing.

Years ago, canned foods grew bacteria. Obviously, if they got too bad then eating them would cause negative effects. However, prior to that, they were great for the bacteria in the gut.