You can use many types of bread for making your sandwich and the filling can be varied and adaptable.The modern sandwiches are prepared with breads coated with condiments and contain a combination of salad vegetables, meat, cheese, and a variety of sauces or savoury spreads.
There is a list of 64 regional sandwich styles in the wikipedia article on sandwich:
Tips for making healthy delicious sandwiches
1- Choose good whole grain sandwich bread, or Pita and 'Lavash' flat bread.
2- Choose low fat cheese.
3- Try vegetable based high fiber spreads.
4- Prepare grated walnut, cheese and chopped fresh herbs in small quantities ahead, and keep refrigerated or use readily.
5- Try chopped fresh herbs and roasted vegetables.
7- Cut your sandwich in smaller portions before wrapping, and keep in cold place.