Even more reassurance... let's look at this the super nerd way... with NUMBERS! Now, if a pound of fat is about 3,500 calories then you would have to eat that much EXTRA over what it takes for you to maintain to actually even gain one pound. It's damn near impossible to gain any real amount of weight in the short term. Anything you do gain (hey, it IS a vacation) is likely water retention from increased sodium intake. As long as you don't go completely crazy, and get back on track as soon as you get home, you'll be fine.