It has nothing to do with air transportation which has been developed in Soviet era, where everebody was equal.
edit: minor mistakes.
https://ru.wikipedia.org/wiki/%D0%A1%D0%BF%D0%B0%D0%BB%D1%8C...
https://www.ozon.travel/help/railway/preparation/trains/
As far as I understand, М has private bathroom but СВ doesn't. It's confusing but I'm sure I saw them sold at different prices.
There were no bathtubs on the trains in 1980-s in Soviet Union...
Stuffed potato is not something Russians eat, least something so popular to be sold on the street. So, again, it was not sold in 1982 or later.
Blinchiki is something that could have been possibly sold since Russians do eat them. I've never seen them sold on the street myself but I cannot possibly say it's as ridiculous as stuffed potato.