A tuna fish sandwich is a food typically made with bread, canned tuna and mayonnaise. There are additional common ingredients added as well, but they vary quite a bit from one recipe to the next. This is a fairly popular food for people in America to eat at lunchtime or as a snack before major meals, and people like it for a lot of reasons, not the least of which are the ease involved in making it and the overall lack of cost for the ingredients. Many people will make tuna sandwiches for themselves at home, and it is also possible to buy them at many restaurants.
When making a typical tuna fish sandwich, an individual normally starts by opening some tuna, typically canned, and then draining whatever liquid it's packed with — normally either water or vegetable oil. After everything is properly drained, the tuna is generally mixed with mayonnaise along with whatever other ingredients are desired, and then added to some bread to make a sandwich.
Many people like to add additional ingredients to their tuna before making a tuna sandwich, and many of these are meant to add little nuggets of flavor to contrast with the tuna itself. For example, it's not uncommon for someone to chop up an onion and mix that with their tuna. Celery, relish, olives, and many other ingredients are often used in exactly the same way. Sometimes these ingredients are even used in various combinations, adding a lot of different textural elements to the sandwich experience.
There are also sometimes other creamy ingredients added in addition to mayonnaise, and occasionally, people add certain flavorings to a tuna fish sandwich. One of the more common examples is mustard, which can add a certain degree of tang. Dry ingredients such as pepper or garlic can lead to a much spicier sandwich without drastically changing the texture of the tuna.
There are quite a few different ways to modify a tuna fish sandwich, such as changing the kinds of bread used. For example the sandwich could be made on white bread, whole-wheat bread, or rye, and the bread may be toasted in some recipes for even more variations. Another way to vary a tuna sandwich is to add toppings such as lettuce and tomato. One of the more popular variations is a "tuna melt," made using melted cheese as a topping, and another popular variation is to pack the tuna into hot dog buns instead of traditional bread, which is often called a "tuna boat."