Exercise exercise exercise usually keeps it vaguely under control for me, and trying to think about stuff a bit more before eating it. You probably will eat more than you do at home, but if you eat less than you usually do on holiday you've made a good start!
But you've got pools for swimming, nice weather for getting out there and exploring on foot and new places to explore, so you may be more active (or at least as active) as you are at home, even if it's in a different way - constant activity instead of intense gym stuff and very sedentary work stuff.
Although it is compulsory to spend some time just sitting on a sun lounger relaxing
I'm off to Marrakesh at the weekend for a few days and hoping to put some of my tips into practice myself, but if not I try to take the view that I can lose a couple of pounds again (because if I gain it won't be much, in context), but I can't easily re-live all my holidays and have all those experiences once I've got home.