When you are walking around Rome and are looking for a nice lunch spot, try the Campo de'Fiori. All along the streets of Rome you will find a number of panini or pizza shops, but if you are in the mood for a different sandwich try Ristocampo.
This little sandwich shop lets you choose the kind of meat and cheese you would like along with a number of vegetables. Suggested sandwiches are on the wall, or you can make up your own. It's a nice break from the pre-made sandwiches you will find elsewhere in the city. Prices range from four to six euros.