Lettuce

Of course the bags of already cut up salad lettuce you can get in grocery stores are the best. However, if they look really nasty or you have to opportunity to pick up heads of lettuce from a roadside stand, here is a quick hint for coring lettuce: slam it down on a counter stem down (best down when you wish it was a camper's head). The core then pulls out easily and whole. The rest of the head can be sliced any way you want.