I think it's been too long since most of us played it.
Good path: snack on undead using eternal rest. There were always undead around, and you could last hit them with the power so they always dropped essences and filled you up.
Non-aligned path: snack on undead or occasional regular spirits, plus regular and frequent use of suppress (summon something first!).
Evil path: devour all sorts of stuff. You would have to use your xp to top yourself off at times, but there were of course benefits.
IIRC only the last one would get you to the state where you could die from sleeping, traveling, etc.