Subway's veggie patties are really good, but not every location has them. They're really good because they don't even try to make them taste like meat. I'm not sure if any of their breads are vegan though.
And many items can be customized to be vegan or vegetarian with some simple substitutions or exclusions. The only problem is when the kitchen makes a mistake. Not a calamity for someone who is just trying to get a lot less meat in their diet, but a reason to be pissed when a vegan wanders into a region of reduced fat sour cream.