Visible crew/equipment: When Annie goes into the shop to ask where Camp Crystal Lake is, you can clearly see the reflection of a boom mic in the window, above the head of the cleaner. (00:07:40)
Visible crew/equipment: When Pamela Vorhees pulls over to pick up Annie we can see a man's arm reflected in the front shield sitting in the passenger seat. (00:18:30)
Visible crew/equipment: When Annie jumps from Mrs. Voorhees' jeep, a white elbow pad can be clearly seen on her right elbow. (00:20:00)
Visible crew/equipment: After they've killed the snake, Alice says "Is it dead?" and as the camera pans up, the boom mic's shadow is visible moving across the wall, directly over Ned's head and the red box. (00:26:05)
Visible crew/equipment: When Officer Dorf gets on his bike and says, "You kids keep your noses clean you understand? You'll be hearing from me if you don't", the reflection of the camera man walking can be seen on the side of the bike. (00:28:05)
Visible crew/equipment: In the scene at the diner after the kids have played "Strip Monopoly" there is a shot of Sandy behind the counter and some customers walking out of the diner. Look behind the last woman walking out and you can see a crew member reflected in the window. (00:46:25)
Visible crew/equipment: At the diner, when Sandy walks to the other end of the counter and talks to Steve, the reflection of the boom mic is visible at the top of the window behind Steve. (00:48:10)
Visible crew/equipment: When Mrs. Vorhees throws Alice onto a table you can see a mattress under it catching her fall. (01:18:35)
Chosen answer: Just after the credits, there's a bank sign that says "Friday, 13 - 7:01 - 60 Degrees". Then the DJ says "It's 7:01 on Friday the 13th of June." and goes on to say some more about it and lists some other bad luck superstitions. At two other points in the movie, two characters (Ralph and Tierney) say "it's Friday the 13th". So there are at least four references to the fact that the movie takes place on Friday the 13th.
Myridon