Dana Gunders, the leading expert on food waste at the Natural Resources Defense Council, is the author of “Waste-Free Kitchen Handbook: A Guide to Eating Well and Saving Money by Wasting Less Food.” The next time you toss out a burger, imagine taking a 90-minute shower. That’s how much water it took to produce that burger and get it to you. Wasting food wastes everything. Americans trash more than one-third of our food supply and…