I liked Jason's proposed definition of "sustainability" based on the impact of current choices on options available to future generations. For example, we could argue about current effects of biodiversity at a particular location, but global loss of species or genotypes clearly reduces options available to future generations.
Week 1 has an exercise on measuring the water content of food. Unless I missed it, there's no explanation of why we should care about water content. For example, is there some implication that water content affects irrigation requirements? It doesn't. Almost all the water used by crops is lost to the atmosphere through leaves. Water content does affect transportation costs ($ and energy) -- hauling tomatoes is mostly hauling water -- but farm-to-store energy use is only a few % of our food system's total (citation on p. 13 of Darwinian Agriculture).