Stan's fight with Luigi, when Stan is about to be dumped in the fried eggs, he already has fried egg stuck to his trousers.
When Olive breaks her glasses during the dance, she must have got them repaired or replaced very quickly as by the rest of the film she's wearing her glasses again.
When the rest of the family are going to the 'farewell ball' near the end, Little Arthur is nowhere to be seen.
At the beginning, after Stan hits the General Manager's car, and starts to pull away, the camera cuts to his cab, and he says "Alright!" There is a green bus visible in this scene. It is stopped, but then it is seen starting to move. This is the bus which hits Stan's bus. The number and destination match up.
At the beginning of the movie the car and green bus that crash into Stans bus are driving the wrong way down a one way street, there are arrows painted on the road and they all point the opposite direction that the car and green bus are travelling.
After Arthur and Olive have rescued the cases and the family are in the chalet, Stan is seen zipping up the suitcase to avoid getting any mud on the carpet. He clearly zips the whole case up, but moments later, the contents spill to the floor, despite their being no hole or any gap for the clothes to fall out of.
When Blakey is leaving after telling the Butler family that the dance night is off, the Butler family can all be heard shouting goodbye to Blakey but they are all standing still and their mouths aren't moving.
Reflected in the bus window, after Stan stops outside the camp gates.
During the sequence when Stan's Mystery Tour bus catches up with and proceeds to overtake Arthur and the family supposedly on their way To the Prestatyn Holiday Camp, they are in fact travelling in the wrong direction.