Tuna salad is typically a blend of two main ingredients: tuna and mayonnaise or mayonnaise-substitute. The tuna used is usually pre-cooked, canned, and packaged in water or oil. Pickles, hard-boiled egg, celery, relish, and onion are ingredients that are often added. When the spread is placed on bread, it makes a tuna salad sandwich. Tuna salad is also regularly served on top of lettuce, tomato, avocado, or crackers, or by itself.