The South Park franchise is based entirely on references to other media, so it's no surprise that there are tons of Easter eggs in The Fractured But Whole. Many of them are insignificant and reference background characters, while some are full-blown references that you don't want to miss.
If you want to see what the five best Easter eggs in South Park: The Fractured But Whole are, then this guide will show you how to find them. Most of them can be seen during the main campaign, but others involve getting into side quests.
In any case, grab your popcorn and make your way through all of them!