Growing our own food.
I grew up in Cloverdale, an area of Surrey that was (once) known for its expansive farms and local food supply. Now it is mostly filled with dense housing and green grass landscapes. I would be lying if I said that I didn't miss the farms. I had friends that lived on working farms, and I visited them often. We also had opportunities to buy direct from farmers on a regular basis, and Cloverdale did not have a Farmers' Market that I know of at that time.
One major theme of my childhood has become my mission as an adult. I grew up with a very large garden at home. We grew so much of our own food, preserved, froze it and completely enjoyed the massive zucchini harvest each summer. I spent many hours each summer shelling peas for the freezer. Definitely a way to keep your kids busy through the summer!
But this upbringing always makes me wonder why people think they can't grow their own. A simple window box of salad greens, a few tomato plants, maybe a little herb garden. All very achievable, and they help in so many ways. Eco-footprint reduced, and you get tomatoes. So worthwhile!