On the other hand, we could use the Barter System and trade goods and services like they used to back in the day. For example, if I wanted to buy food from someone, I could trade them for a service, like a haircut or help on building their house. Although, using this system would be difficult in big cities, almost chaotic. It would be hard to keep track of all the transactions taking place, and some trades might be unfair compared to others. However, it is a very sufficient system.
Either way, with no cash, we would have to agree on another system to rely on.