It might look like we have made a pretty useless system here. But really,
there isn't that far to go before it can do some work. One of the first
things you would have to do is have the root filesystem mount read-write.
There is a script from the SysVinit package, in /etc/init.d/mountall.sh
which does this, and
issues a mount -a so that everything gets mounted the way you
specify in /etc/fstab. Put a symlink called something like
S05mountall to it in the target's etc/rc2.d.
You may find that this script will use commands that you haven't installed yet. If so, find the package that contains the commands and install it. See section Random Tips for clues on how to find packages.
Look at the other scripts in /etc/init.d. Most of them will
need to be included in any serious system. Add them in one at a time,
make sure everthing is running smoothly before adding more.
Check the File Heirarchy Standard (see section
Filesystem).
It has lists of the commands that should be in /bin and
/sbin. Make sure that you have all these commands installed.
Even better, find the Posix documentation that specifies this stuff.
From there, it's really just a matter of throwing in more and more packages
until everything you want it there. The sooner you can put the build tools
such as gcc and make in the better. Once that is done,
you can use the target system to build itself, which is much less complicated.