Could 3 days of vacation/eating out make you gain a noticeable amount of weight?

Yes: Some of it may be water weight.

Run the numbers: a pound gain/loss is roughly 4000 calories==7.5 big macs. I test produced all beef finger food to eat 2-3 BME's (big mac equivalents) in one sitting and still be able to eat that much again to demonstrate the possibility of gaining 2-3 pounds in that period of time. Can also easily occur in disease states (dialysis, heart failure). Mostly, no, just changes in fluid/stool accumulation.