If you're not abhorrent to a little cheating, if only to get yourself back to the surface, you should try TooManyItems (by "Marglyph"). After you get it set it, if you press 'O' on your inventory screen, you'll toggle a graphical list of every material in Minecraft. Clicking on one will give a number of that material to your inventory.
If you ARE abhorrent to a little cheating, then this is still an excellent option. In addition to getting free stuff, you also get the options to Save up to 7 inventory configurations, and delete items permanently from your inventory.
So what I'd suggest, is that you save your near-empty inventory, give yourself enough material to get back home, and then reload your old inventory.
To set it up, simply download it (18.01Kb), extract everything in the folder, and then copy the craftscripts folder, minecraft.jar, and WorldEdit.jar files directly into your bin folder for Minecraft. If you can't find the hidden file, the default is
C:\Users\UserName\AppData\Roaming\.minecraft (Replace "UserName" with your username).
Note: You will likely have to enable the viewing of 'hidden files and folders' on your machine, as AppData is hidden.
One word of warning: This mod is very quick/easy to set up, but it requires you to overwrite the minecraft.jar that is already in your bin folder. If you want to remove the mod afterward, all you need to do is copy the original minecraft.jar somewhere else, and then once you're done with the mod, delete the craftscripts folder, and WorldEdit.jar file, and replace the new minecraft.jar with the original one.
Updating the game will also remove the mod, as it will update your minecraft.jar file, but it won't remove the craftscripts folder or WorldEdit from your bin folder. However, leaving those two items there will not affect your game at all, so updating your game is a much faster way to remove the mod from your gameplay.
REALLY IMPORTANT EDIT: With 1.5, this method of installation no longer works: you need to append the class files of the mod into the minecraft.jar file. If you're unsure how to do this, you can simply download a copy of the already modded minecraft.jar Here.
/killcommand only works on smp servers. It doesn't work in single player mode...