So that last post was the practical, down to earth info on organics. This is the eagle's perch view.
I'll spare you the details, but lots of things we do to mass produce food are unpleasant or have bad side effects. The Green Revolution upped bushel/acre numbers, but it also stripped whole countries of their top soil, ran us through a lot of fossil fuels, and poisoned the world's flora and fauna. Movements like the organic movement are trying to step back from that, but with demand rising due to population increase and affluence in population dense regions like India and China, we can't functionally go organic on a mass scale. Organic farming works in microcosms, but with the world situation, not in macrocosm right now.
From a macrocosm perspective, the most helpful thing the average guy can do is eat less meat. If every person ate a typical north american diet, and distribution systems were uncorrupted and set up well, we could feed 2.8 billion people on our currently cleared arable land. If everyone was vegetarian, we could feed 10.2 billion people the same number of calories and full nutritional spectrum. As there are more than 6 billion of us, we can't all be north americans in our diet or half the planet starves. Alternatively, we could pay more for our meat - grass fed cattle are a carbon hazard, but don't hurt the world food system or demand more of the amazon be chopped down for corn/soy meal. Grass fed beef is more expensive for a reason, it takes several years more to grow them to full size, a lot more overhead for the rancher than a factory farmed soy fed cow.
I understand there are few willing to go full monty, even just cutting meat to once a day or once every other day would help a lot, if done in mass. Different animals waste different ratios of their calorie intake. I'm doing these numbers off of memory, but the priority order is right: beef is the most wasteful, conveying to you only 10% of the calories it took in per lb, pork is in the middle at 25%, and chicken is the clear winner at a nearly 50% conversion rate. (These apply to corn/soy fed factory meat, not your cousin's dairy farm, a local hog raiser, or a grass fed ranch.)
Fresh water is the next tacky issue, ignored by many for now in my country. (UAE is actually paying attention, and doing ok, but we can't all use desalinazation plants.) Constant new purchases of bottled water have drained US aquifers - the biggest one is down to 20% and will take at least a thousand years to refill. Cheap gold is also something to avoid, as it is often obtained by blowing the glacial tops off of mountains, lowering rainfall in previously lush regions. Manufacturing of any kind is water intensive at some point, so just buying less stuff would help.
Anyhow, being a good citizen of earth is pretty much impossible to do right, you can only do your best. Even that is a life work in and of itself!