It is difficult to eat healthy while traveling. There is going to be some amount of going off track, but here are some tips you can use so you do not go completely off your health routine.
Carry some whole fruits, like an apple, or an orange- that you can peel and have almost anywhere. They are not difficult to carry, and make a filling snack.
Make a healthy sandwich with whole wheat bread, and carry that with you. Alternatively, think of some other healthy snacks that are easy to carry and easy to eat.
Try asking for a vegetarian diet. This will probably lead to fewer calories, and will ensure that you get some fresh fruits and vegetables.