I have used LaTeX for more than a decade, but still don't own a copy of the LaTeX Companion.
Update: I now do!
8 How to sort a .bib file with biber? Sep 24 '15
3 How to sort a .bib file with biber? Dec 24 '15
2 Can WhizzyTeX be used with XeTeX? Dec 13 '12
2 How to use \autocite with biblatex-apa? Mar 29 '13