You can't put on 3 or 4 pounds of fat in a day unless you overeat by 10-15 thousand calories. If you are doing that, then you have bigger problems than the number on the scale.
Short term weight fluctuations are caused by fluid retention caused by all sorts of things like eating salty/fatty food, your menstrual cycle, exercise or what is hanging around within your digestive system. Nothing at all to do with gaining fat, which is the only thing you need to be concerned about.
Therefore taking scales on holiday is madness and tells you nothing. Scientifically it is better to weigh yourself every day, but each spot measurement is only accurate within a few pounds each way at best and tells you little about how 'fat' you are.
Victoras advice is good. Be mindful about what you eat. Have nice but healthyish food in sensible portions, rather than using being on holiday as a reason to stuff yourself with crap. Be active - walk, swim, play sports.
That's what we do on holiday because it's what we enjoy and despite drinking quite a lot of alcohol and eating what seems like a lot of nice treaty food, I usually stay the same weight within a pound or two, because I'm more active and eat better than I do at home.