Fair question, what are the rules?
1) When the ghost dies, you start over from scratch. This means you don't get any of your old stuff, even if by some magic it happens to still exist. Write it off, and enjoy a pristine character! (I think this is actually the most exciting part of the game, starting a new character)
You'll note that the ghost does keep his key unless he dies. If you manage to surface the ghost, you're certainly still entitled to use the key to get your backup gear.
2) If a character dies, (but not the ghost) and decides to surface, you can give them up to 1,000 au. (Adjust upwards for higher levelers, if you like). More than this, and you could trigger the audit flags, and get him removed from play, unless he manages to build enough experience up very quickly.
3) Don't give things of value away. Sell them. This keeps the game in balance. Charity is a nice trait, but it destroys the game balance very quickly. Besides, you might need the extra wealth sooner than you think.
4) Ghosts should not be playing with live characters, except in a rescue situation for the ghost. This is used to abuse AI bugging, and if you're discovered, both characters will probably be starting from scratch.
5) Don't pkill without a decent reason. (Note that "I wanted his stuff" is at times a decent reason, but farming level 1 characters is just mean

6) Don't house artifacts. Artifacts are rare, and precious things. They do not like being stored in houses. It's ok to keep them if you intend to use them in some reasonable period of time (think days, not months).
Courtesy rules: Not manadatory, but might keep you from being fruitbatted by an angry mage.
7) Don't litter in town. using k takes exactly the same number of keystrokes.

9) Don't afk in shops.
10) Don't save in the dungeon above level 600. surface first. You might come back to discover you're entombed in solid rock anyway.
Question/Comments welcome. This is just a tentative initial list. It will most likely change a bit with some feedback.