You can rehydrate droopy greens by letting them sit in cold water for an hour or three. Be sure to drain them well before putting them away, though. This can work for certain other vegetables as well.
Many leaf vegetables such as lettuce store longer if there's a little bit of water at the bottom of the bag so the stem(s) can "drink," but the leaves must be kept clear of it or they'll rot. In some cases, like with asparagus, this is best achieved by putting them in a rigid container with a little water in the bottom, vase-style. Unless you're going to use it right away, though, drop a plastic bag over the whole thing to keep the moisture in.
