Your choices for fast food:
Wendy's - pretty good, but obviously no where near as good as rib eye steak or fillet mignon.
McDonalds - Has pretty clean food, but REALLY bad ingredients. (They use artifical pink slime that is made from chicken bones and fat to make their nuggets)
Burger King - Their food actualy isn't that bad, the meat is "OK" quality meat, and it's even healthier because it's grilled. But Burger King is notorious for having very unclean ingredients, that carry E Coli bacteria.
Subway: Their ingredients may be better and cleaner than most of the competition, but they aren't really as "Fresh" as their slogan would imply.
If I were you, I'd just eat fruit (from a healthfood store, otherwise monsanto will be all over it) and turkey for lunch, occasionally having other things that aren't as good for you.