Kefir
Kefir is a culture, coming from the Northern Caucasus Mountains. We make it in water, but it's traditionally made in milk.
DOM's kefir page has a lot of info on kefir.
The way we use kefir:
Old kefir is cleaned with a sieve and water, keep the cleaning water in a bowl. Take 12 thee spoons (preferably not iron) from the kefir and put it in a 3 liter jar.
Add 4 dried figs, 200gr sugar (cane or brown sugar), 1 lemon cut in two. Then add ca. 3 liter water.
Let the kefir stand for 2 or 3 days, at room temperature.
Filter the kefir, lemon,.. from the liquid with a sieve. Squeeze the lemon and add the liquid to the kefir liquid.
Clean the kefir with water using a sieve, keep the water in a bowl. If you want you can add the cleaning water to the kefir liquid to make it more but thinner.
Make a new kefir mix.
The amount of kefir grows every time, you can eat the kefir that is to much.
As for real food, I believe it's interesting to look at which cultures/groups/tribes had or have good health, and see what they eat. There's for example Weston Price, who visited a number of these kind of villages and studied what they ate. Most of the people hadn't even ever heard of a toothbrush, while most of them didn't even have a hole in a tooth in their whole life. Wether or not their diet was the foundation for their health, it certainly was part of their healthy lifestyle. And adopting a similar diet is necessary to be healthy, eventhough there are many other things like spirituality, environment, social relationships, etc. that have a big role concerning health. What this "paleolithic" diet means in short, is eating what you can find yourself in nature and eat without cooking (so that excludes sugar, factory food, grains, beans, ..). In some way you could call it our natural diet, the diet of hunter gatherers. By the way, once you start to learn all the stuff that is edible in nature, you wonder how it's possible to starve, and why there are hard working farmers? When you just have to be open to receive what mother nature wants to provide to you. Although I think planting my own food in horticulture style, something like Masanobu Fukuoka's natural farming, isn't a bad idea in these circumstances.