http://www.wtsp.com/news/story.aspx?storyid=25442 (links to news video and text)
In short: a 12-year-old did a science fair project where she compared the amount of bacteria in fast food restaurants' ice to the amount of bacteria in their toilet water. The toilets were cleaner 70% of the time.
My DH always rolls his eyes when I insist on no ice in my soda when we eat fast food. It's for this exact reason.
The article mentions restaurants reusing garlic bread and rolls. I've heard that you should tear up or otherwise visibly "ruin" any food you don't eat for this exact reason.
While I suppose you are welcome to do what you want with food served to you, I hardly think it's the patrons' responsibility to assure the restaurant doesn't re-serve the rolls!
Maybe my response is colored by knowing my share of dumpster divers, but I am fine with leaving uneaten food untouched.
My grandpa was one of those people who would not order spaghetti when he went to an Italian restaurant, but if it were on the Chinese or English restaurant menu, he was all over it! And universally disappointed (and no, this was not because he had Italian dishes he liked better -- he'd order the hamburger there). He never understood what he was doing wrong that he was always the disappointed one.
I find it best not to order things like lasagna or casseroles because they dry out over the course of the day. I'll make an exception for quiche or frittata in the morning, but not generally after noon unless it's a great place or I'm in the mood for rubber.
Soups, on the other hand, are a large-batch dish that holds up great in many cases.