Um. That can't really be answered briefly. You can't even say 'everything in coreutils' because that doesn't include vi, sed, grep, find, etc.
Anyway - most everything in /bin and a good chunk of /usr/bin and, depending on whether you have root access, ditto for *sbin.
Another way to look at it is to check out the shell & utilities part of posix.
A lot of those aren't actually used much, but many of them are essential.
Maybe if you said why you wanted to know or what sort of commands you were looking for...
-- Oh, and welcome to LQ (and apparently Linux itself, as well).