In an effort to reduce impact, we've tried to avoid buying too much fresh produce that's not produced locally. It's certainly not the 100 mile diet, but that vast majority of the produce we ate this winter was either canned (mostly by us) or frozen. It seems to me that you'd get better tasting food for less energy if you preserve produce at it's peak and ship it preserved rather than try to ship fresh food around the planet.
There are some obvious costs to preserving food. Canning requires a fair bit of heat, and frozen foods require refrigeration. But it gets worse for frozen foods. Apparently, even the non-CFC refrigerants are nasty and being emitted in mass by supermarket freezers. They don't kill the ozone layer, but the are potent greenhouse gasses. Wonderful. At least there are alternatives, it's just that most places don't use them.