I put butter on one piece of bread when making a salad sandwich... mayo on the other... preferably real mayo but a good shop bought one is ok. Cailin is right, the order of things is important on a salad sandwich... lettuce needs to be next to the bread to stop moisture making the bread soggy... never put beetroot and tomato beside each other or else the sandwich will slide apart in your hands... preferably separate with some grated carrot or sprouts.