Manga Meat
It's revealed in Wano that Luffy's Gear 5 is the awakening of the Human-Human Fruit: Mythical Model: Nika, however this form has been hinted at as far back as this Arc in the manga.
What is Skypeia?
Since Strong World, Oda has been involved in the stories each animated film of One Piece has, even making certain characters in the films canon. However, on this character has been shown out right in the manga AFTER his animated debut.
Who is Shiki The Golden Lion?
This live action One Piece actor taught himself near fluent Japanse as a THIRD language to interview Oda himself.
This is Chopper's favorite food.
What is Cotton Candy?
This famous professional wrestler "sees" himself as a One Piece fan.
Who is John Cena?
What character, besides the members of the Straw Hats, has Oda put into each Arc of the manga as an easter egg?
Who is Panda-Man?
This famous American musician performed cover of "How You Remind Me" and "Bad Reputation" for One Piece Film Z.
Who is Avril Lavigne?
This famous actor has been cast as Sir Crocodile for Season 2 of One Piece.
Joe Mangeniello
This fruit was grown in Nami's childhood home.
What are Tangerines?
The Straw Hat logo appeared in the final panel of this MEGA famous manga as graffiti as an homage to Oda as the author's way of saying goodbye.
What is Naruto?
What famous French legend inspired Sanji's tragic backstory with his biological family?
Who is The Man in the Iron Mask?
This mostly accepted One Piece anime filler arc was the only arc to hint at concepts in a future canon arc in the manga.
What is the G8 Arc? (Navy Base after Skypeia, shipwright in the base hints as things Franky will bring up in Water 7)
While Jamie Lee Curtis didn't get the role of Dr. Kureha due to scheduling conflict, this voice of this famous animated spaceship captain gladly took the role when offered.
Who is Turanga Leela? (Futurama/Katey Sagal)
This is the food Trafalgar Law refuses to eat
What is bread?
While never revealed in the actual story, Oda did reveal in an interview this name for Zoro's mother.
Who is Terra?
There are many famous inspirations for characters in One Piece that inspires Oda's designs. None more so than with Franky who inspired by this famous Canadian Actor.
Jim Carrey
A popular filler story in the anime is the Chopperman episodes, one of which featured voice work from this famous Japanese professional wrestler.
Who is Minoru Suzuki?
The One Piece Live action showed this fight which was only alluded to in the source material.
What is Zoro vs. Mr. 7?
This reactor and game streamer actually went on to voice the character Trebol in the English Dub of the Dressrosa arc.
Who is Alejandro Saab (KaggyFilms)?
Which of Luffy's brothers was techincally first shown?
Who is Sabo? (confirmed by Oda to be in the crowd in Loguetown when Luffy fights Buggy and Alvida, you can see him from the back when Luffy is about to be executed by Buggy)
Mayumi Tanaka has been the voice of Monkey D. Luffy from the beginning, however, she was known for voicing this famous Dragonball character before she put on the Straw Hat.
Who is Krillin?
When Luffy sees the wanted posters for the first time with Koby in the live action, it hints a multitude of characters like Buggy, Foxy, and this future Straw Hat Grand Fleet captain.
Who is Cavendish?
What is Takoyaki (Octopus fritters)?
This NBA team recently made a deal to use One Piece as a sponsor.
Who are the LA Lakers?