There is little chance the Standard is gonna get updated again, especially since CDR (the Common Lisp Directory Repository) kinda stopped. That said there are a few libraries that are kinda considered to be the default go-tos for various needs:

CL-PPCRE for regular expressions.

Bordeaux-threads for threads.

Alexandria for various miscellaneous stuff.

Trivia for pattern matching.

CFFI for, well, FFI.

And Series for functional iterative sequence-like data structures.

There's also ASDF and UIOP, but I'm not sure whether or not they're part of the Standard.