Rocket's Eye

This wasn't exactly an Easter-Egg; it was more of a reference to the previous Guardians of the Galaxy movie. In that movie, when Rocket came up with a plan to stop Ronan, he said that he needed a cybernetic eye that belonged to one of the Ravagers. Of course, he was joking at the Ravager’s expense, and didn't actually get the eye.

In Vol. 2, Baby Groot is tasked with bringing Yondu his fin, and he comes back with various unrelated objects, including the cybernetic implant. So, although Rocket didn't get the eye when he first requested it, he got it in the end. This was too bad for the eyeless Ravager, who wound up dead at the hands of Yondu.

Again, this isn't an Easter-Egg, but it shows that James Gunn put quite a bit of effort into establishing continuity between the films.