I end up buying the salad mixes at the wholesale club at times too. The big bags. I regret it though because even with a family of 5 it goes bad a few days after it is open and taste very chemically.
I keep thinking about getting those green bags. I have heard from many people that they actually work very well.
Hey IC here is a trick for you. If you put a paper towel in with your greens it will soak up the excess moisture and keep them good longer but if that still doesn't work for you try getting spinach instead of spring greens this way you have more ways to use it up. It could be a salad, or a side dish when sauteed, you can throw it into omletes or pasta on a pizza, it's endlessly useful.