… is a matter of taste, but this is (part of) my list:

# For general use:
apt-get install aptitude zsh less strace psutils rcs screen \
                rsync sshfs ntpdate host exim4-daemon-light \
                sudo file bc mlocate man [uemacs|nano]
# For systems running on the "bare metal"
apt-get install smartmontools
# For server maintenance
apt-get install munin-node munin-plugins-extra sysstat
# For development use
apt-get install dpkg-dev debhelper devscripts patch liburi-perl \
                fakeroot build-essential autoconf bison \
                autotools-dev sharutils

At least for uemacs you need to access the /usr/local repositories. This /etc/apt/sources.list.d/usr-local.list will do:

This is outdated

deb-src http://debian.usr-local.de/debian sarge local non-free contrib
deb     http://debian.usr-local.de/debian sarge local non-free contrib
deb-src http://debian.usr-local.de/debian etch  local non-free contrib
deb     http://debian.usr-local.de/debian etch  local non-free contrib
deb-src http://debian.usr-local.de/debian lenny local non-free contrib
deb     http://debian.usr-local.de/debian lenny local non-free contrib
deb-src http://debian.usr-local.de/debian lucid local non-free contrib
deb     http://debian.usr-local.de/debian lucid local non-free contrib

deb-src http://debian.usr-local.de/debian gutsy         non-free
deb     http://debian.usr-local.de/debian gutsy   local non-free contrib
deb-src http://debian.usr-local.de/debian oneiric local non-free contrib
deb     http://debian.usr-local.de/debian oneiric local non-free contrib

This is outdated

APT::Default-Release "squeeze";

To change the timezone of a running systems, issue

tzconfig

or

dpkg-reconfigure tzdata

depending on your version of Debian.

update-locale LANG=C LC_CTYPE=de_DE LANGUAGE

sudo apt-get install devscripts
apt-get source <package>
cd <packagedir>
# generating new changelog entry with local version suffix for distribution lenny:
export DEBEMAIL="${DEBEMAIL:-peter@foo.bar}"
export DEBFULLNAME="${DEBFULLNAME:-Peter Foobar}"
dch -l .ul~lenny -D lenny
dpkg-buildpackage -rfakeroot

Linux Debian