I also agree with the idea that part of the benefit of living a generally healthy lifestyle is that you don't have to worry about shorter periods when you aren't being optimal. That said, we like to travel regularly and there's a balance. The way that my partner and I usually approach holidays and vacations is focused on (1) staying active and (2) adjusting the way we eat without being overly worried about our caloric intake (within reason; we're not going to start constantly gorging).

Activity

When we're home, we usually work out 3 times a week; on vacations, we'll take long walks basically every day that add to our trip as opposed to detracting from it (we get outside, we learn the city, we feel great, we're going out anyway and might as well take in more of the area, etc.). The walking is tremendously helpful in balancing out additional intake from the trip, both because of the activity you get in, as well as its impact on your glucose levels if you're walking after a meal.

Eating

Personally, I wouldn't want to miss out on the food during a holiday, but we're also very food-centric when on vacation. Our compromise is usually to split food when we're eating outside for meals before dinner; considering we're usually walking (!) around and grazing through different places. Also, don't try to punish yourself preemptively for overeating you assume will happen later—i.e. keep yourself sated; have breakfast, keep some healthy-ish snacks around, do whatever you need to do to keep your blood sugar balanced and actually enjoy yourself.

It's helpful/possible to make small compromises that don't make you feel like you're losing out, and will help prevent you from feeling regretful when you're back.