You could do 2 lines - 'old school' like cheese and pickle, ham and cheese, chicken, bacon and mayo, blt etc. Then a modern recipe line with your more cosmopolitan ingrediants.
Just to add - I agree with the poster above about the quality of the bread being equally as important as the ingrediants. If you can't make your own try to source from a local baker. I used to work in the office of a 4 shop bakery and we had over 50 sandwich shops and canteens we supplied with bread and rolls. Any bakery should be happy to bring samples and sort a business account.
One more thing (while I think of it) that bloody annoys me is picking up a roll that looks full only to find out that there is only filling hanging out and not stuffed throughout the roll properly. It's the oldest sandwich trick in the book (pile stuff in the middle and then cut it in half showing the 'full' filling) and you'll find it done in nearly all the supermarket sarnies and rolls. So, don't get a reputation for being bloody stingy on the filling. One thing that will keep peeps coming back is value for money. Of course the quality of your fillings and how much you put in the roll will all impact on your pricing.