Get (or update) minecraft:

mv -f minecraft_server.jar minecraft_server.jar-`date +%Y%m%d`
wget https://s3.amazonaws.com/MinecraftDownload/launcher/minecraft_server.jar

Get (or update) craftbukkit:

mv -f craftbukkit-0.0.1-SNAPSHOT.jar craftbukkit-0.0.1-SNAPSHOT.jar-`date +%Y%m%d`
wget http://ci.bukkit.org/job/dev-CraftBukkit/promotion/latest/Recommended/artifact/target/craftbukkit-0.0.1-SNAPSHOT.jar

Get the Essentials plugin from this forum post or this wiki. To install the core pack and group manager, as of right now you can do:

cd plugins
wget http://tiny.cc/EssentialsZipDownload
unzip EssentialsZipDownload
rm EssentialsZipDownload
wget http://tiny.cc/EssentialsGMZip
unzip EssentialsGMZip
rm EssentialsGMZip

For full control, add your name to "ops.txt", e.g.

echo "myname" >> ops.txt

If you installed Essentials Group Manager above, you can configure it by changing "plugins/GroupManager/config.yml" or "plugins/GroupManager/worlds/world/*.yml". To confirm, editing these files by hand sucks, as does the usability of CraftBukkit in general. ENJOY!

In these scripts, set M to the amount of RAM to allow, in megabytes.

Vanilla server:

#!/bin/sh
M=350
java -Xmx${M}M -Xms${M}M -jar minecraft_server.jar nogui

CraftBukkit:

#!/bin/sh
M=350
java -Xms${M}M -Xmx${M}M -jar craftbukkit-0.0.1-SNAPSHOT.jar nogui