I'm looking now at the 2012 season, and that was a bit controversial as everyone seemed to have a secret. So, if we're basing it off that, here's what some of the secrets might be:
"Before moving to Australia, I campaigned for Donald Trump"
"I am a parkour expert"
"I'm a bastard, literally. My parents aren't married."
"I sold my virginity on eBay"
"I was in a film that won Best Picture at the Oscars"
"I'm chronically unemployed"
"I'm a chess grandmaster"
"I'm an undercover detective"
"I am hyperthymesic"
"I was born a woman"
"I was born a man"
"My girlfriend is a former student of mine"
"I was expelled from 10 different schools before graduating high school"
"I was part of a cult"
"I was excommunicated from my church"
"I'm a Venezuelan refugee"