All you can do is muster every ounce of will power you have available to avoid the most unhealthy of foods. Then, pray to God that you don't gain any weight until you can get home and take control again. Yep.
But here are a few ideas to help minimize the damage you do to your body while traveling.
I packed this food to travel with in the car: fat free popcorn, wheat checks, multi grain cheerios, 100 calorie bags of cookies, carrot sticks, water, and my weight watcher's calculator. My water was replaced with diet Coke at the first stop, and I didn't eat any carrot sticks :-)
Don't think to yourself that you're not going to eat while you drive on a long car trip. You are going to munch while you drive, and there's nothing you can do about that, so just try to bring some healthy stuff with you so that you don't buy chips and candy at the gas station.
Stopping for lunch? Your fast food options are pretty much between Subway or Taco Bell (and when I say Taco Bell, I mean you better be ordering from their "Fresco Menu"!) or a salad from Mickey D's, but that's impossible to eat while driving.
When you get where you're going, go grocery shopping if there are no appropriate snacks where you're staying. Don't eat Doritos and little Debbie cakes.
As for now, I'm hoping my weight has stayed the same. My mom's scale is reading more than my scale at home was, but it can be different scale to scale, right??? (Can you hear my denial about gaining back some weight?) At least I've been trying to get some exercise! :-)