Aang's glider and Sokka's boomerang from Avatar: The Last Airbender (2005) can be seen on one of Rex Igneous' piles of treasure at around 14:03.
In the scene where Rex has been given the gifts by Rayla/Ezran/Callum. The camera pans across to Rex' treasure horde and lying amongst the treasure you can see Sokkas Boomerang and Aangs glider from 'The Avatar - the legend of Aang' animated series also written by Aaron Ehasz.