> banking was non-existing in practice

There was a consumer bank (Sberbank) where you could store your money. Besides the risk of the state just keeping it (which also was real - the Soviet state never played fair) the problem was getting the money out would involve going to the office of the said bank, standing in a long line there, dealing with famously friendly (not) Soviet service, etc. So it was an option when you needed to store or retrieve a lot of money, not when you needed something day to day. And of course nothing like personal checks or personal credit or anything like that existed, so in day-to-day affairs, cash was always the only way.