Revealing mistake: The two Jeeps running during the tour are supposed to be automatically moving along the track in the road but several shots reveal there is nothing connecting the Jeeps to the track.
Continuity mistake: When Grant and the kids wake up in the tree and Grant feeds branches to the dinosaur, Tim's position is an absolute chaos: He is either seated or standing; close to the dinosaur's nose or chin; far away or very close. There's no continuity whatsoever.
Continuity mistake: After Hammond says "Welcome to Jurassic Park" Grant is facing the jeeps, 3 meters away, with Ellie 5 meters to his right and Hammond 3 meters to his left. Grant then turns his waist around to the left, though his legs still face the jeeps. In the wide angle everyone has changed positions drastically: Grant's legs have magically turned 180° and Hammond is not only opposite Ellie but very close to her.
Continuity mistake: After Hammond says "Welcome to Jurassic Park" Alan is sitting on the floor with Ellie comforting him. A shot later she's gone, only to reappear 5 metres away in the next shot.
Continuity mistake: Ian gets out of the car to distract the dinosaur. Inside the car, he's nice and dry, but the second he gets out of the car, he looks like he's stood in a bathroom shower for ten minutes.
Revealing mistake: When Tim is looking at the 2 cups of water vibrating due to the T-Rex's stomping, you can see a very small dark spot at the bottom of the cup, which is actually the knot of a guitar string that was plucked to create the vibration effect.
Continuity mistake: When Nedry's car is stuck in the mud, he goes out front to grab his winch and pulls out a fair bit of wire. In the next shot, we see that he has a lot less wire than before, even though we never heard the winch retract.
Chosen answer: They all left on the same boat Nedry was trying to get on with the embryos. You can hear Samuel L Jackson's character announce that the boat will be leaving at a specific time and everyone had to be there or be left behind.
Shannon Jackson