Does organic make a difference? As a rule of thumb, I encourage clients to steer towards the most seasonal, local and organic ingredients because, quite frankly, they taste better than conventional, imported ingredients. Admittedly, in many cases organics and conventional can be similar. However, with vegetables like lettuce, where water is the main component and soil is integrated into the leaves, organic is definitely your best choice.
When you bring the lettuce home, keep it loosely wrapped in a plastic bag. Fold a wet towel around the base of the lettuce if you want it to last longer. I also like to wash the lettuce and wrap it in a towel, dried completely. My mother, an expert shopper, found very cool Lettuce Bag that keep the lettuce fresh for a few extra days. A Salad Spinner also is a very useful item for storing lettuce in the fridge. (That is, if you have a full-sized fridge to fit it into. Unlike moi!)