Gremlins

The time machine prop from The Time Machine (1960) can be seen behind Randall Peltzer (Hoyt Axton) when he's on the phone with his wife, while attending the convention. A moment later, the machine has disappeared (into the future or the past), to the astonishment of several on-lookers.
Also attending the convention were Steven Spielberg, Jerry Goldsmith, and Robby the Robot.

Chinese Boy: Look Mister, there are some rules that you've got to follow.
Billy Peltzer: Yeah, what kind of rules?
Chinese Boy: First of all, keep him out of the light, he hates bright light, especially sunlight, it'll kill him. Second, don't give him any water, not even to drink. But the most important rule, the rule you can never forget, no matter how much he cries, no matter how much he begs, never feed him after midnight.