Too bad cl-ppcre is extremely slow in my experience, but that's what we have. ASDF and UIOP are the same as the rest, de facto standards, but not ANSI nor CLtL.

I would also add iterate to the "must haves". All noobs should constantly look at the CLHS (available for dash, zeal and emacs too!), https://lispcookbook.github.io/cl-cookbook/ and https://github.com/CodyReichert/awesome-cl, anyway.

Truly, someone could tie himself to SBCL and its extensions and get a much more modern environment, but I think it's worth targeting ECL and CCL in addition.