Taking the sad opportunity that my pi crashed "irreversibly" (I suspect SD corruption, almost all was good except that I lost wifi access, some services stopped starting at boot and even that I investigated almost every single directory or file that should be responsible for boot/network config I couldn't find a solution; happily I had backup of everything important + this blog :)) and I had to perform clean install I will make a list of some most basic linux tools that do not come shipped with standard raspbmc installation but I find very useful:
sudo apt-get install and then:
git
htop
mc (midnight commander)
screen
tree
The above list will grow over time, as I install, test and get addicted to more "essential" tools :)