They are all "probiotic' foods, that supposedly contribute to good gut flora. So the thing all those foods have in common is that they are fermented.
Natural sauerkraut is fermented cabbage. Most pickles are just soaked in spicy vinegars, but originally pickles were fermented, which made a rich brew of bacteria and yeasts. Sauerkraut is the German version, Kimchi is the Korean version. Kombucha is fermented tea, which is made with a bacteria and yeast combo called a "Scoby". Kefir is fermented milk, similar to yogurt. Miso is fermented soy beans.
It's controversial whether any of the micro-organisms make it into our lower intestines, because our stomachs are very acidic, which kills almost everything. Still, a lot of people swear by naturally fermented foods. If you try kimchi, be careful because it can be spicy-hot, and that could be irritating to your rectum.
You can get kombucha and kefir from places like Whole Foods (I don't know where you live, but any grocery that sells a lot of organic foods should have those things). I would look in an Asian market for kimchi and miso. Sauerkraut I don't know.
Here's a link that might be useful:
http://www.nutritionletter.tufts.edu/is ... 383-1.html