Since it was brought up about celeb's deaths preceding a show the celeb appeared on obviously prior to death, I'll keep the maudlin train running with the unfortunate death of Randy Amasia the very same day that his $25000 win arrived at his house, and unfortunately he didn't see it.
Okay, now some happier ones...
On Eubanks' Card Sharks, there was a contestant related to Florence Griffith Joyner, and there was an educated guess question about how many total miles she ran in a week or something like that... he knew the exact number. Bob laughed at the producers' reaction.
Then there's the lady contestant on TPIR, a double amputee, who was playing for a treadmill. (Roger told me a while ago that if something like that happened when he was there, they would've quickly substituted a more suitable prize, but this lady didn't take any offense and kind of thought it was funny.
Not sure if this qualifies, but Bob Barker found it amusing that Patricia Bernard, the lady in the bathroom, was to bid on a waterbed.
On TPIR from the early hour run, a male contestant with a shirt that said "Lover" was playing for a new bed.