Is your lettuce wilted, pull off the leaves and put them in a bowl of cold water. Peel a potato and put it in the bowl, half an hour to an hour and your salad is just as fresh as the day you bought it.
Wash the lettuce well under the tap, I will always petal by petal, dry the lettuce in the salad spinner, grab a big plastic bread bag and do all the lettuce in there. Keep the bag open, swinging through the air and lay there like a knot. Now you have a kind of balloon filled with lettuce. Put it into the fridge, so the salad days remains good. You can also continue to play a bit of lettuce and then close it again in the same way.