I've got a brilliant box from Tupperware - I can't remember the name but its got two little holes in one end and you have either both closed, one open or both open depending what veg you have inside. The bottom is ridged so nothing sits in any wet which forms. I've got all different sizes, and mushrooms keep for nearly 2 weeks without going soft, and a bag of salad about 1 week.
Our Sainsbury's has just started selling "living salad" - like the pots of growing herbs but "cut and come again" varieties of lettuce, so that should last longer.