BusyBox is what is called a multicall binary. Meaning it is one binary that has multiple utility functions. If called as a shell it runs as a shell, if called as the
ls command it runs the ls command.
It acts as a replacement to many standard tools used on Linux and Unix-like systems with a small memory footprint. It replaces the functionality of other software like GNU coreutils, util-linux, iproute, etc and its intent is usually to be targeted to the requirements of a specific embedded system.
Therefor if the desire is to have a package manager of utilities in fact.. this is what busybox replaces and is designed not to be. So you can simply use the suite of tools busybox replaces.
You can select which utilities are included in busybox when you build it during compiling. Its not intended to be configured after the fact.