First off, don't skip breakfast. Instead, make a healthy meal a part of every morning. Include some low-fat protein, fresh fruit, or veggies and whole grains. A bowl of healthy cereal and some fruit is a great choice. Save the treats for lunch of dinner.
When you head out, take some healthy snacks with you so you won't be tempted by junk food if you get hungry. Nut sand either dried or fresh fruit are great choices.
Try to do some cooking during the vacation. It doesn't have to be elaborate, keep it simple. Stop by a grocery store when you're getting close to where you'll stay.
Eating out is part of the celebration of being away and it's alright to indulge, a bit. If you splurge, keep it to one meal a day and be sensible about portion sizes.Look for healthier choices on the menu, just because it's lower in calories doesn't mean it won't be tasty.