For a dinner party several months ago I made Lynne Rossetto Kasper's Salad of Tart Greens with Warm Balsamic Dressing (from "The Splendid Table"), using the quantities in the ingredients list as I was expecting six people for dinner. The yield was huge, about twice what we needed for dinner, so I stored the leftover salad greens (undressed) in a big steel bowl, covered tightly with foil, in the refrigerator. I was very pleased to discover that except for the basil the salad greens stayed fresh and crisp for days and days.
Since then I have made a habit of mixing up a big bowl of sturdy greens, such as romaine, red-leaf lettuce, frisee, radicchio, parsley, and curly endive. If the greens are washed and well dried in a salad spinner, then torn into bite-sized pieces rather than cut with a knife, they keep for up to ten days in the refrigerator. I haven't kept a bowl of greens more than ten days, but on the tenth day the remaining last serving of greens was still crisp and fresh. Even the parsley kept its fresh quality.
What a revelation this has been! By spending a couple hours every ten days or so I'm able to have a fresh salad whenever I want without having to go through the effort of making a fresh salad. I always made a practice of washing salad greens and storing in the refrigerator, but never actually prepared the greens for a salad before I made this salad. It is just such a time savings to scoop out servings of the torn and ready-to-eat greens, and it allows me to spend more time on the rest of the meal. I often supplement the greens at serving time with a handful of arugula and torn basil leaves, adding toasted pine nuts at serving rather than tossing with the greens.
This is such a great alternative to having to resort to bagged salad greens. Making the investment of a few hours yields a such a huge benefit for me; just wanted to share this tip.