310: Which feat is it that allows a character to go into -15hp before dying, rather than -10hp. I thought it was diehard but it isn't...
This is probably not what you're looking for, but this could work in a pinch for you. Shape Soulmeld (Rageclaws), Magic of Incarnum. Use that soulmeld. Now you can act normally until -9 hp (believe you still die at -10, as usual). That's quite boss for a level 1 character. Now invest essentia into the Rageclaws soulmeld. Per point of essentia invested, you can last another 3 hp.
1 essentia = act normally until -12hp, 2 = act until -15hp, 3 = act until -18, etc.
So if you have essentia points (taking an meldshaping class, being an incarnum race, or taking incarnum feats), the Rageclaws soulmeld will pretty do what you want to do.
But it takes essentia to get you to acting normally at -15hp, which is a little more investment than just 1 feat (either a race, class level, or another feat), so I'm pretty sure that is
not what you were asking for, so everyone consider this question unaswered. Still, it might work in a pinch and I though to might find it interesting.