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.
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.
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.