I didn't grow up in a city that had an MLB team, so I always found myself following specific players more than anything. Like all kids of the 90s, I loved Ken Griffey Jr., Frank Thomas, Barry Larkin (settled on being a Reds fan when Griffey was traded)....and Jeff Bagwell.
I had the chance to go to the 1999 All Star Game at Fenway, and I made sure to go see batting practice before the game. When Jeff Bagwell took his turn, I ran down to behind the third base dugout with my program, and as he walked back to the dugout I asked if he would sign my program. He looked up and said "hang on a sec, kid." And he disappeared into the dugout.
For a few seconds I thought "whoa, I think I got stood up by one of my favorite players". Just as I was finishing that thought he popped back up and said "Here you go." and handed me his bat.
To this day it's my most prized possession and the one possession I'll never give up. If you zoom in you can even see Fenway Park grass on the pine tar.
Talk about a core memory. I'm not sure if players know how much stuff like this truly means to kids, but I've always wanted to thank him for this.