Well, well ... I've just picked up Sailing on the Seas of Fate for Elric!, and Mark Morrison has his own simple rules, but I'm not sure I buy the 'timing'; for example,
Thirst - After 7 days without water, lose 1D4 HP per day
Hunger - After 15 days, lose 1D3 HP per day.
In both cases HP lost in this way can only be replaced by eating and driking.
Its a bit of a brutal, simple system, but I don't agree with the long period of leeway given. And no effects of hunger, etc. Of course we are looking at something playable versus a complex simulation.
I do like the reduction in HP. BUT, having two types of HP reduction would get very .. messy. I propose a system where death is reached at ever increasing levels. So normally, death occurrs at 0 HP. Take 3 points of HUnger or Thirst, means that now, you die at HP 3. Three days later you suffer 4 more points of Hunger, and now you will die at HP 7. Its a bit like 'Hit Points taken off from the opposite end. So a guy fighting to cross the desert, battling cliffs, monsters and sandstorms, as well as hunger and thirst, is effectively 'burning the candle at both ends.'
This seems simpler, and moe realistic.