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.
Revealing mistake: When Ellie is running to the shed, the same clip of her jumping a tree is seen.
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.
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.
Continuity mistake: When the baby Dinosaur is hatching, her arm comes out but in the very next shot it's her head that is coming out. (00:27:30)
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