It might be a bit late for this, depending on how in-shape you are and when the trip is, but the best piece of advice I can give is work on your body as much as possible. Having a good body makes people so much more attractive in my opinion.
It's not just your body that changes, it's your face too. You lose fat from your face and the structure of your face changes. It becomes a lot more chiselled/defined.
There are no short cuts really. You can suck your cheeks in, stick your neck/jaw out as much as possible and find your best angle, but it won't change what you look like in real life. Just get fit and healthy. Train hard, eat clean, transform yourself. And then you'll feel like every photo is a good photo. Not just 1 out of 100, where the stars aligned and the lighting/angles were right.
But make sure to exfoliate (once or twice a week at most) or your moisturize won't really help.