In his book Debt, David Graeber completely crushes the Econ 101 myth that before money people used a system of barter (eg one cow for four goats). Such a system only works if you already look at things in terms of a standard unit of measurement - money. What people actually tend to do in non-monetary societies is give favours. In a small community, it is easy to do a favour for someone with no expectation of immediate recompense. You know that it will balance out eventually, and if it doesn't, the moocher will be socially shunned. It also enhances the social network by making everybody essentially in debt to everybody else. Barter and cash societies involve finite transactions. Debt lengthens these transactions, requiring a relationship between the lender and the borrower. However, that relationship is an inherently unequal one and has a goal: the debt being repayed. Because of the nebulous nature of favours they can go on infinitely and never require one party to be subserviant to the other. I just so happen to need a place to stay, and you will offer to host me. Next time you are in my town I will host you. You can see how working on a culture of favours rather than debt would make for a happier, more equal society.
I personally find this idea fascinating because I come from the kind of small communities that still value favour-based relationships. I can recognize these behaviours in my large extended family. There is always the implicit understanding that if you need something and we can help, we will. When you expand the circle beyond just extended family to family and close friends of extended family, you can start to see how a community can be formed and everybody's needs met just through working together. I tend to assume that everyone I'm friends with falls within this circle of favours, so it becomes: Alice needs a place to stay in a city where Zelda lives. I ask Zelda to host Alice on my behalf. Zelda knows, through this web of trust we've built with favours, that Alice is trustworthy. Alice then owes me a favour and I owe Zelda a favour, but Alice and Zelda are now connected by that favour. Of course, my assumption that everybody I know is willing to be so open with their belongings is usually untrue. We do live in a large world run by cash, rather than a small community based on a mutual survival. However, if you've ever wondered why some places have better hospitality to strangers than others, I think this is the reason. Visit New Brunswick some time and I'll give you a first-hand experience.