Go to the scene where the scientists, the lawyer, and John Hammond are on that "ride". When Grant (Sam Neill), Ellie (Laura Dern) and Malcom (Jeff Goldblum) push away their lap bars and rush out of the ride so they can get into the laboratory, we see Grant's hat sitting on the seat that had been next to him. You can clearly see that Grant, Ellie, and Malcom have rushed past the seat that has the hat on it, and therefore none of them had picked it up. In the next scene when they are in the laboratory (the scene when the Raptor's egg hatches), Grant's hat has magically returned to his head!