I would like to add some tools and not just kernel modules into the initrd (initramfs-based). Now I'm aware of how to unpack and how to pack the initrd with cpio and have even written a hook for /etc/initramfs-tools/hooks in the past to integrate a third-party kernel module. However, while the available script libraries seem to be geared towards the integration of modules, none of them seems to be for integration of other entities (in particular programs and their dependencies).

What options do I have to automate the integration of some useful tools for recovery into the initrd? I'm talking about the "rescue" system that the system drops into if it is unable to mount the root drive given to it by the boot loader.

Please note that I don't want the SquashFS approach as is used for Live-CDs because for the issue at hand it will be by far sufficient to include some relatively small tools that aid in recovery of the system (when it gets stuck in initrd and can't boot further). Also, the machines when they run into the issue that we have had in the past tend to boot into the rescue system, but there a few tools are missing to kick the system back on trail ...