EaseCopy (https://aescripts.com/easecopy/) is about the plugin I use the most on AE. It's so simple, and so useful I can't even imagine anyone that doesn't have it docked in their workspace. Forever.
It's free too!
I'd say it should ship standard with After Effects. I hate that even the simplest plugin is a hassle to install on my work machines because of IT bureaucracy. I honestly have a list of free plugins (and a few paid ones - Overlord anyone?) that I believe should all come standard with AE. But since one idea per topic, this one is for EaseCopy.