When traveling for conferences, this is probably my chief complaint. It is incredibly hard to find good, fresh, food in a lot of places. With conference centers in downtown areas, there usually is not a close grocery store, which is very irritating. At times there may not be anything but fast food or mediocre chain restaurants.
I've basically learned that a well-done burger from room service, while it costs more, is probably tastier and cleaner than what you'll find in most places.
Sushi is a go-to for me when traveling to large urban areas. Look for a highly rated, clean, place that does maki rolls, for extra protection choose a protein that is actually cooked (like shrimp) or tofu. Any place where you can get steamed white rice and a protein grilled or cooked in front of you is probably better than Taco Bell. And when in doubt, Chipotle has the freshest veggies one can find.
I traveled to Vegas a few years ago and it was miserable, how hard is it to get fresh vegetables on the Vegas Strip? Apparently, all but impossible. I finally found a Chipotle buried in a strip mall, highest quality food I had on the whole trip (I was on a very tight grad student budget).
I now do not travel without protein bars. Too many nights curled up on the floors of hotels after eating bad food. I'd rather ration a Clif Bar and water than deal with shitty food followed by food poisoning, at this point.