You don't. It's like Minecraft. You can do almost everything in Minecraft alone and everything exists in infinite quantity, so why trade in the first place?

This goes both ways. Let's say there is something you want but you're having trouble obtaining it. You'd need to give something in exchange.

But the seller of what you want doesn't need the things you can easily acquire, because they can get those things just as easily themselves.

The economy collapses back into self sufficiency. That's why most Minecraft economy servers start stagnating and die.