I have travelled alot in my time, especially travelling overseas. My advise to you is simple.......
That's what holidays are for....HOWEVER.....as long as you don't over do it, that is eat like this.....
Whenever possible, try making "better" food choices, ie. vegies, salads, just not too many....you don't want to be on a holiday which feels like a "fat farm" or slimmer's bootcamp!!!
And all the walking around sight seeing, and generally moving about doing stuff whilst away, should help balance out any small gain. And even if you do gain a little, it makes running on the treadmill when you get back much more tolerable because you have wonderful memories you can drift back to and daydream about which will help take the focus off the numbers that are painfully slow in counting down!!
Strong people don't walk away from the truth, only the excuses others try to sell them.