Way too many to list here, but I'll offer a few that had some personal significance.
Back in 1961 my father took me with him to look at components to set up a high end stereo set up so he could enjoy his Tijuana Brass, Beethoven, and Don Ho in the comfort of our new home. He headed over to the Sound Shack, which I recall having some Tiki styling to the interior, and was considered the top stereo electronics store in LA at the time. So Pop's looking over receivers when LA Dodgers pitcher Sandy Koufax walks up to look at receivers, and the two of them get into a conversation about stereo gear. After a few minutes, Pop introduces me, Koufax shakes my hand, they go back to discussing stereo a bit more when Koufax excuses himself as he as to leave, and Pop gets back to assembling that stereo.
Fast forward to the fall of 1961 and this adorable tot gets picked to be a guest on Art Linkletter's House Party, a hugely popular show at that time. Linkletter is largely forgotten today, but back then, and for decades after, his was one of the most influential voices in the US, an author, journalist, humorist, radio and television host.
Part of the show's contents included an interview with 4 kids, who would be asked for their opinions on a pre-chosen topic.
This time around the question was, "What would you do if you were president?". Linkletter would stand next to each of us, holding out the microphone for us to speak into. The responses were pretty much what you would expect from kids. One little girl said that se would give everyone a "horsie", another piped up saying he would "give everyone free ice cream!". Linkletter gets to me and asks me what I would do if I were president. I look him squarely in the eye, then turn to the camera and say, "I would solve the Cuban Missile Crisis".
Total chaos as the audience erupts into applause and cheers. Linkletter is frozen like a store dummy, mike still outstretched, mouth hanging open, staring at me. Someone yells "stop rolling", and the crew just waits for things to calm down. Once filming is resumed, Linkletter tries to make a humorous response, but I don't recall what it was, and the segment was over. After wrap, we were taken to the Brown Derby for lunch. I had the lucious lulu burger, with fries, and a chocolate shake that was made table side. We also got some gifts, including a Hokie Pokie cotton candy machine.
Collaborating with Ray Bradbury while working on Something Wicked This Way Comes was a high point, and later, the production threw me a birthday lunch, and Ray attended. We ended up shooting the shit over a couple of hours, just on our own. That was a nice treat.
Dinner with Zubin Mehta was fun, helping Henry Fonda with some hardware store purchases, almost colliding with Paul Newman while exiting a parking lot (he was in the right), giving a tour of our little 4 walled VFX studio to Jane Curtin and Dan Aykroyd while making Coneheads, both of them as nice and curious as can be, sitting in the green room at the Hollywood Bowl and discussing music with John Williams, walking the set of the Next Generation Enterprise bridge and meeting many of the cast, while I was at Paramount, are among a few most memorable of many memorable encounters.
As for sightings of celebs? Hundreds if not thousands.