Masashi Kishimoto put a One Piece skull and crossbones (along with the straw hat) on the very last page of the last chapter of Naruto: on Naruto’s face on the Hokage Rock, Boruto paints the Straw Hat Pirates’ jolly roger, a reference to One Piece by Eiichiro Oda.
In return, the cover art of One Piece’s chapter 766 references Naruto by Masashi Kishimoto as a tribute to Naruto’s ending.
Luffy eats ramen (Naruto’s favorite food) with Chopper on his head and Nami as a waitress with a Konohagakure design changpao at a restaurant. A little fox eating ramen and wearing an Uzumaki sleeveless shirt is seen among them. There’s another character sharing Luffy’s table, eating meat (Luffy’s favorite food) but it is covered by Nami so his face is unseen; however, due to his clothes and size it is heavily implied that it is Uzumaki Naruto himself. The One Piece logo is different in this chapter, with the O in a Konohagakure symbol shape, the first E holding a shuriken and the classic I in the form of Luffy now resembling of Naruto.