Yeah, kvas is everything. We have plenty of brands which are sold in grocers. Right now, a 2-liter bottle of kvas is standing on the table downstairs (i guess, mom is sipping it
). When i was little, my granny used to make kvas from scratch, and later, during Perestroika, she was making it out of special brickets. Nowadays, very few russians make kvas from scratch.
Kissel is our heritage too: my favourite one is cranberry kissel. My dad used to make it himself. It's sold in grocers either, but most varieties are for naught. OTOH, its making process isn't hard, so sometimes we make it at home.
Well, the third traditional russian drink is "tea fungus" (the one that you call kombucha). People grow it at home (we were doing it either), and it reaches enormous sizes (the fungus' body, a.k.a. scoby).
The most traditional dish with kvas is "okroshka" (cold soup made with kvas instead of water). Some people use kefir. There is such a variety of kvas as "white kvas". Lol, my sister's husband says that it has a repulsive taste. But i made okroshka with white kvas, and it was more than edible.
Anyway, we love our fermented foods and drinks. (Even those who don't care about traditions, make sauerkraut, fermented cuckes and "soaked apples" at home).