In Spain, there are two types of small meals which Americans would refer to as sandwiches. But while sandwiches are on many Spanish menus, they're not quite the same thing as bocadillos.
Differences Between Bocadillos and Sandwiches
In Spain, a “sandwich,” which uses the English word (but is pronounced with a Spanish accent, "sand-week") is made with modern-day white bread, which is called pan de mode in Spanish. Most often these sandwiches are served in cafeterias and available cold or grilled. A sandwich is definitely not considered much more than a snack in Spain.
The second type of sandwich is the traditional bocadillo, made with a rustic barra de pan or baguette-style bread loaf. Bocadillos are served everywhere from taverns and bars to cafeterias, roadside establishments, and at home. However, you probably would not see a bocadillo on a restaurant menu. If you want something more than a snack, a bocadillo will do the trick.
In Between the Bread
When it comes to the sandwich filling, neither the sandwich nor bocadillo has much more than meat, ham, cheese, omelet, or tuna. In general, the Spanish do not add lettuce, pickles, onions, mayonnaise, or "secret sauce" to a bocadillo—they are simply meat, tuna, cheese, chorizo sausage, or omelet between two pieces of bread.
Sometimes the bread will be moistened by cutting a tomato in half and rubbing the cut side of the tomato onto the bread, or drizzling a bit of Spanish olive oil onto cut side of the bread—or both. Bocadillos can also be cold or hot.
Differences in Flavor
The bocadillo might not sound as appealing as an American sub sandwich, but what it lacks in ingredients, it makes up for in taste. Most Spanish sausages, cold cuts, and hams are very flavorful and easily eaten with just a slice of bread.
They are also very portable when traveling. Because bocadillos do not have lots of mayonnaise or lettuce and tomatoes in them, they are not as messy or as likely to spoil in the heat. Bocadillos are great to take on a weekend camping, hiking, or biking trip, or to eat for an afternoon snack if you are touring a new city on foot.
Many Spaniards regularly prepare their favorite bocadillos to take with them on the bus or train to hold them over until they reach their destination and can eat a proper meal. Bocadillos also are slightly more popular than sandwiches as the mid-day meal among Spaniards who work outside the home.
Typical Bocadillos in Spain
Because the cuisine of each region in Spain is so different, typical fillings for bocadillos will vary from region to region. Omelet bocadillos are a popular option for an easy, portable breakfast, typically including eggs and cheese, as well as a variety of fillings like potatoes, beans, chorizo, and peppers. Meat bocadillos may be prepared with chicken, pork, or beef, as well as regional favorites like goat or horse. Fish bocadillos are also popular and can include squid, sardines, cuttlefish, and other delicacies.