I thought about this last night. When you kill an enemy then a "life module" is dropped {maybe showing in-game as a spark on the ground}. If you're down in HP and you step on the spark then you get up to 10 HP - and the spark would disappear {one time use kind of thing}. If you're only down by 5 then that's how much you get, if you're down by 15 then you only get 10. But if your HP is full then nothing happens and the spark remains until someone who is down on HP steps over it - or until the end of that round.
I suggest a spark so it can easily be seen and used. Though, of course, someone of questionable character could use it as a trap for the unwary, hiding off to the side and ambushing anyone who expects to gain back a bit of their HP. But no one here would be that dastardly {heh, heh, heh}.
