There is no such thing as a sustainable part of an unsustainable whole, and a society that labels certain specific practices or techniques "sustainable" has a sustainability problem. For example, organic produce is only sustainable when we have sustainable ways of getting it to consumers, who must have sustainable forms of income with which to buy it. The whole system must be sustained, or it will eventually fall apart, rendering its "sustainable" parts unsustainable.
Sustainability is a challenging concept. It reaches well beyond the simple choices of individual consumers to buy or not buy certain "sustainable" products.
The global economy's departure from sustainability came gradually, but one of the major developments was a shift toward unsustainable forms of agriculture. As the hazards of this shift became clear, some people sought a return to "natural foods" - previously called, simply, "food" - and formed cooperatives to access those foods affordably. These co-ops were based on each member having an equal vote, and on profits being returned to members based on how much they spent; this was based on principles that had been developed over more than a century. These co-ops spread and grew, and eventually played a role in returning natural foods to the mainstream.
Now, organic and "sustainable" food is big business, to the point that some worry that the organic movement is being undermined. In any case, most of the movement has been captured by its former adversaries. In some cases - like shelf-stable juices - a single corporation dominates an entire product category in most natural food stores; Smucker's owns Knudsen's, Santa Cruz Organics, and After the Fall. Over in the fridge, Coke owns Odwalla and Pepsi owns Naked.
Meanwhile, an increasing share of the organic industry's product is distributed through investor-owned distributors and sold through investor-owned stores. This makes "sustainable" products ultimately unsustainable, by shifting the profits away from the altruistic entrepreneurs who started these companies, and toward investors who are primarily out for profit.
This shift concentrates wealth in progressively fewer hands, which is clearly unsustainale. If you need to see this for yourself, just play Monopoly (owned by Hasbro, which now owns Parker Brothers, which ironically bought up the rights to this and other commercially available versions in order to corner the market on what started as a home-made educational tool on the drawbacks of the landlord/tenant relationship - but that's another story).
The game ends when more than one player goes bankrupt; the pieces go back in the box, and everyone goes back to their lives. But in the real world, there is no end and no way to start over. So how do we stop our real-life game before it reaches its unhappy end in which most players are bankrupt?
Italy shows an example of how to start: That nation's cooperatives provide almost 20% of all packaged groceries sold in the country. This federated system - Coop Italia - is cooperatively owned by 155 consumer cooperatives with almost 1300 outlets. In turn, these are collectively owned by about 10% of the national population. These members have the opportunity to serve on a committee that approves new products, all of which meet strict quality and ethics guidelines, and some of which provide organic fair trade products at costs rivaling their less sustainable counterparts.
Italy's experience can't simply be copied to the U.S., but there are many other models in which consumers have taken back control of what they consume. This isn't enough to solve the entire sustainability issue, but it is a key part.
We can do this here, too. And we must do this here. We need to get to work and devote ourselves to an economy that doesn't concentrate wealth in fewer and fewer hands. If we don't find ways to make the overall structure of our economy sustainable, nothing else can be sustained.