Here are mine, in descending order of importance:
Video Speed Controller - changes the speed of (almost) any video; press 'd' to speedup 0.25 speed ('s' for the opposite) and 'r' to reset back to 1.0 speed
uBlock Origin - lets me permanently block specific page elements - it brings me joy to block the 'trending' and 'news' tabs, google doodles and any other trendy/ing elements. My 'filter' list is only 100 lines long; mostly youtube, twitter, and stack overflow.
SponsorBlock for Youtube: crowdsources the timestamps for self-promotion and product placement in youtube videos and automatically skips them for you
Duplicate Tab Shortcut: gives keybindings to open the current url in an adjacent tab (rather than at the end of the tab bar).
Others (I don't consider these essential):
SelectorGadget, Pushbullet, JSONVue, Google Docs Offline
One of my favourite plugins is Markdown New Tab. I use it as a better version of bookmarks for the things I use regularly, as well as to keep notes. I also have it pinned so it's always available in a predictable location without starting a new tab.
Another one I have, but don't use too often is TinEye Reverse Image Search. It's one of those things that is awesome to have right there for when you want to find the original source (or maybe even just a better source) of an image.
SSH Agent for Google Chrome MindMap Tab Chromebook Recovery Utility