Most of these are retcons, Oda most likely did not have these planned right from the start...but it still shows Oda's attention to detail at times.
From Chapter 1! Shanks staring down the Lord of the Coast.
(Chapter 1)
...And then YEARS later, we find out that was probably Shanks using Conqueror's Haki. Plus, the fact that it was his arm with his Abyss Mark that got eaten.
Then during Baratie, with Mihawk talking about "Hunting Rabbits".
(Chapter 51)
...And then YEARS later, we learn about the Celestial Dragons "hunting rabbits" in their Games.
(Chapter 1096)
And probably the most infamous example. Luffy doing what we would find out MUCH later is the Nika Dance in Skypiea.
(Chapter 253)
More recently, when Doflamingo mentioned the National Treasure of Mariejois.
(Chapter 761)
...And then YEARS later, after putting the pieces together, that National Treasure is probably Imu himself. And Doflamingo wanted to put his mind inside Imu's body with the Op-Op Fruit's Personality Transplant ability. Imu wouldn't even appear until chapter 906.
Plus, there's the way Oda sneaks in little "jokes" into bounty numbers and chapter numbers, using Goroawase number puns. I didn't even realize he was doing that until around Wano.
reddit.com/r/OnePiece/comments/jnp7z6/odas_little_jokes_on_the_bounty_numbers/
And there's probably other stuff that hasn't been revealed yet that I feel like could eventually be revealed to be foreshadowing. There could be a lot of stuff like this, scattered all over the manga.