I seem to have found two that no one online has mentioned, one is during the scene where Hiro is trying to do come up with an idea for the showcase, is you look closely at Tadashi he is reading a comic during his line "Woah washed up at 14, so sad." If you look close enough you'll realize it's actually the Big hero 6 comic.
the other one just makes me laugh, when Hiro smuggles Baymax up to his room in his lower battery drunken state, when Hiro is explaining to Aunt Cass he has "a lot of schoolwork" to catch up on if look in the background there's a photo of Mochi dressed up as a certain beloved disney Alien Stitch!!
I looked no one has mentioned these yet I just thought they were awsome!