It's tricky to make good choices on the road, but you can keep up the spirit of Box Lunch Lifestyle: better is...better. For example, try finding a grocery store or Walgreens/Duane Reade over your lunch break. If you can't find vegetables, you'll almost certainly find fruit. Only canned? Fine. Still better, especially without added sugar or corn syrup. Yogurt, string cheese, and deli meats are quick "better" choices, too.
Use your lunch time to think about or try something new based on where you are. If you're traveling for work, a break from work thinking to do something for yourself is healthy. If you're on vacation, just enjoy yourself. Consider taking a break from all your normal routines if that's what's best for you.