Well -- let me think of them all -- not while caching, but I've met a few people you may have heard of.
When flying home from Marine Corps boot camp in 1977, Omar Bradley was on the same plane as I was. Of course, as a PFC it was hard for me to approach him, but I did!
I've played trombone for 40+ years, and I was in a "pickup" band for Frankie Valli once. The Fireballs were on the same concert, and in fact, they live in this area. I never knew! And of course, the recording studios here in Clovis are the ones made famous by people like Buddy Holly!
I've met or emailed with well-known trombonists around the world, too -- people like Denis Wick, Doug Yeo, etc. Of course, if you're not into "high-brow" music, you may not recognize these names. Oh, JJ Johnson, too, God Rest His Soul.
Met the Mangione family on an airplane once -- I approached Chuck, told him he looked a lot like someone, and we really like the music "that guy" produced! He was really happy to have a perfect stranger tell him that.
And I went all through school, from 1st grade through high school, with a guy named Steve McMichaels -- you can read a little about him here -- he got his nickname because he used to imitate the character with the same name from the Blazing Saddles movie. He was a good fighter back in high school, too, but don't ask me how I know!
But not while caching -- I tend to try and be as private as possible while caching. Usually if I see another person around, I wait until they're gone or I can't stay any longer, in which case I skip the cache.