I think that alot of it will be glycogen (carbohydrate stores)which packs lots of water, bloating from extra salt, sugar, alchohol ect, and maybe even stidge left over in your intestines.
Of course you will have also gained fat, how long was your holiday? If it was a week, you would have had to eat about 5000kcals a day to put on 7 pounds, which is difficult. If it was two weeks, then it would be easier and you would have only had to eat about 3500 kcals a day, which is manageable on hols!!
If you put this in reverse and say that you were going to lose 7 pounds in two weeks (of actual fat)and your daily expenditure was 2000kcal then you would have to stick to about 500kcal a day to lose it. (3500kcals per pound of human fat stores).
This would probably slow down your metabolism as 500 kcal is very very little, like anorexic little, and you would not burn calories as fast anyway. That's why it harder to lose than to gain!
I'd say aim to lose 2 pounds in a week by eating loads of salads and fruit, no alcohol, no junk or stodge ect. That would be quit easy. The rest should melt off quite well over a few weeks with moderate calorie restriction (-500kcals a day, so 1500ish). Good luck!