I often feed the same salad for a week straight and switch it up each week. I just go with what looks fresh at the store each week and rotate based on that. I do advise offering more than one item in each salad. I would go with 2-3 items from this list each week
http://www.beautifuldragons.com/Nutrition.html From your list bok choy, collards, turnip and mustard greens are excellent staple greens. Cilantro and kale and carrots are OK when mixed with a salad occasionally but I wouldn't use them as staples. I usually buy a squash (yellow, zucchini, acorn, spaghetti, whatever you want really) or a bag of green beans, or a bell pepper as well. Those usually last about a week when I cut them up to add to a staple green for a salad.
I feed the leftover salad and any veges that look to be going bad to my bug colony or will eat myself so there really isn't much waste. I've also found that I can keep the greens for a pretty long time if I rinse them, cut them down to remove the stems, then put them in a big ziploc bag with a folded paper towel in the fridge. I can often keep them fresh for two weeks that way. Keeping the veges fresh for longer will save you money on replacement as well.
Another method for storing fresh veges is to chop/shred the salad portions into small bits and pack them into ice cube trays and freeze them. That way you can remove a cube or two (Depends on the size of the tray I suppose) to put into a salad and it's ready to go on demand. I haven't used this method but others have with good success. That will give you even longer term storage of prepared salads while still allowing you to provide a good variety of options.
