You just give. This idea of free loaning is totally counter-culture. It blows down the icons of society, because, if one thinks about it, a lot of those icons have to do with money and its conventions. But here we're talking about a society that doesn't have competitive or materialistic goals as its root value system. It's simply about people helping people.
Nursing mothers donate extra milk, which is then frozen until it is needed.
There are even volunteers who undertake certain dietary restrictions in order to produce milk that can be given to babies suffering from allergies. Aside from all the practical and communal benefits of free loans, there is a deeper spiritual element as well. God Himself is constantly engaged in sustaining all of Creation through His infinite acts of kindness. The Sages say that the world came into being so that God could bestow His goodness on others. We are the recipients of that goodness, and when we act in a like manner by doing kindness for each other, then we are emulating God.