The best place to buy iceberg lettuce is the farmers' market, where specimens have been picked within the last few days or even hours. Look for heads that are dense and heavy: if you're planning to serve the leaves intact, as in a wedge, it's best to buy dense heads that are firm when squeezed. Since iceberg consists of about 96 percent water, it's important not to store the lettuce in the coldest part of your refrigerator, where the leaves may freeze. If you use only part of the head, wrap the remaining section loosely in a paper towel and seal it tightly in a Ziploc bag; stored this way, it should keep for about five days. Although many people discard the tender yellow core and leaves, we find that their crinkly texture and appealing bitter edge make for great pickles and soup garnishes.