I've recently come back from a holiday in Cyprus, it was only a week but I did put on a few pounds, in fact I probably put some of them on before I left as I had quite an indulgent weekend. However I found that as soon as I got back into my normal routine I lost two of them quite quickly.
The thing to remember with holiday weight gain is that it doesn't have to be permanent. Obviously the less you gain the better, but as long as it doesn't have time to "settle in" you should be able to get rid of it quite quickly.
Sometimes we go on holiday with the intention of gaining weight because we imagine we will go mad with food, but that doesn't always have to be the case. A few years ago I went to Mexico and it was all inclusive with a beautiful buffet every night. I would always assess the buffet first and then go for what I really fancied with the intention of going back for other things, but I found that by the time I had finished my plate I was often satisfied and I had no desire to be bloated and over full, especially knowing that this lovely food was available all the time.
When I returned home I was exactly the same weight as before I went. This proves that it is the expectation of deprivation that makes us gorge food when we think we have a 'free pass' like a holiday. It's always good to be able to let your hair down when you are away but we don't have to go berserk with food.
One of the main reasons we do gain weight on holiday is lack of exercise, this is OK for a couple of weeks, it's a good idea to get moving when you get home though, it will help shift the pounds quicker.