The Egg is an important symbol within the world of Ready Player One, because it represents multiple things. The Egg represents power because the one to find it will get lots of power, as well as become a multi-billionare, while also gaining lots of respect from people for being the one to be able to overcome all the obstacles placed in the competition, and winning something so huge and significant. The Egg also represents the journey in which all gunters and sixers participated in, the journey towards their shared goal of obtaining The Egg, and all the hardships and memories made along the way.
The IOI symbolizes evil corporate greed and power in how they only see things for the financial profit they can make off of it with Wade stating that "The moment IOI took it over, the OASIS would cease to be the open-source virtual utopia I'd grown up in. It would become a corporate-run dystopia, an overpriced theme park for wealthy elitists." Throughout the story, the IOI use countless evil tactics to try and one up gunters. at first it started out with something small, like just piggybacking off other gunters, or bribing them to get information, but throughout the story, they become more and more violent, by killing people that cause trouble for them in real life such as their assassination of Daito where, despite it being murder, they were easily able to frame it as an "otaku suicide."
The IOI can also be seen as a symbol for slavery, with how they take make people fear them so that the IOI can control them, and with how they how they have indents that end up getting stuck working for them for their entire lives, never to be able to pay off all their debt. The way the IOI treats indents as well shows how their greed with how they see all their indents as human resources, by calling them by the number given to them rather than their actual names.
Quarters in the book symbolize the accessibility of games, where regardless of how big the game is, all you need is a quarter to start, just like in The OASIS, where Wade says that all GSS asks of you is a quarter when you sign up, meaning anybody can play.
In the book, Wade is awarded an artifact, for completing a perfect game of Pac-Man, which is a quarter. This quarter also symbolizes accessibility, but it also symbolizes power because in the end of the book, the quarter gives Wade an extra life, symbolizing how you don't need to be super rich or powerful just to take part in somthing as big as this competition.
Avatars in Ready Player One represent the player's best qualities and how they change from who they are in real life, to who they are in the OASIS. Avatars are a symbol for change because in the game you also level up and get better gear, so the Avatars represent the change people go through as they play and it also symbolizes the journey with how the avatar of Wade changes from being a poor, generic looking avatar, into a very powerful avatar with lots of money and gear, who later becomes Anorak when he wins the competition, gaining the ultimate power, and freedom to do whatever he likes.
All pictures are taken from the movie so they will not be 1:1 visual recreations of the book