"We could do small things that would make a big impact," said Stein.
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They purposely shop in a store which boasts that the food sold is grown locally.
"It's really great that people are caring where the stuff they are buying and eating comes from," said Harroun.
What does sustainability mean? The USDA tells us there is no official marketing definition, but the main concepts are: people, planet, and prosperity.
"It's that a product or a company from farm to table is doing everything they can to really protect the assets of our planet," said Phil Lempert, Food Industry Analyst.
Is there enough locally-grown food? Is the soil being protected? Are farmers making enough money to support their families and workers?
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There's also the question of what items in your local store are sustainable-- and that can be challenging.
There are a few ratings systems like "How Good", which evaluate products on their sustainability.
"Since there's no marketing definition for sustainable, it's hard for consumers. We've got to look when we're in the supermarket what claims might be made on that package. If you're really concerned about sustainability, you want to go to that company's website and really read up what they're doing," said Lempert.
A store, which specializes in sustainable said it faces its own challenges.
"What we're doing is exciting and people love it, but it doesn't mean it's easy," said Josh Blaine, store manager.
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Locally grown produce means many items are seasonal; and then there's the cost.
"It can be more expensive to source local products because we're working with smaller scale farms; we're also working with people who are trying to do right by the environment," said Blaine.
But shoppers like Harroun and Stein said it is worth doling out more green to go green.
Food experts say it is likely Congress may have to initiate the first steps in order for the USDA to make a marketing definition for sustainability.