James Dyer has a useful short post on indexing his init.el file. His scheme is simple. His init.el is broken into sections each of which starts with
;; ;; -> Section-name ;;
Then he used occur to generate the actual index. Rather than call occur each time with the need to provide the regex, he wrote a 4-line function that does it for him. He doesn’t say whether he bound it to a key sequence but that, of course, is trivial.
One of the commenters suggested using imenu. That’s would have the advantage of having the results show up in the echo area rather than a separate buffer but it’s not clear that that’s the right thing. You might want to visit more than one section, in which case having a (semi) persistent index is a win.
Regardless, using imenu instead would be an easy change, especially if you’re using counsel-imenu. For simplicity, though, it would be hard to beat Dyer’s short function using occur. The nice thing is that with either solution you don’t need to install anything (other than a short function): everything you need is already there.