@Vordak: Well, if your power is manipulating carbon allotropes, thats actually really powerful on it's own considering Graphene alone is rather magical. But it also wouldn't be as OP as it seems, if you start to consider the limitations that even exotic materials have.

[hider=InLong]Firstly, unless your entire body is made out of Lead, then radiation is still problematic for you. You can't be walking into nuclear reactor cores and then be walking out unscathed. Even if you didn't care about cancer, radiation poisoning is still not good for you, and if you constantly munch on mutant radioactive fauna, you'll be quite exposed to that. Luckily, any organic material is made out of carbon so you don't have to go out of your way to find it. Still.

Secondly, I'd say having hardier bones and muscles will not make you super-strong. You won't have enough force to lift double-decker busses, even if you wouldn't be crushed by the weight. You'd still be much stronger than average, but to a more reasonable extent. And you would be more durable, but not absurdly so. Any damage you do take is still going to heal at the usual rate, or require very unique resources.

I might as well mention that diamond is very good at cutting things because of it's hardness, but is also very brittle, and breaks easily, if I remember my science classes correctly. Cuts and punches, might not be such a big deal. Bullets, hammers, and very forceful impacts on the other hand, are rather nasty.

Thirdly, there's plenty of things even the strongest of acids won't dissolve, so while you could eat a wider variety of things, you won't be eating everything. 

Lastly, in spite of the apocalypse thing, a lot of knowledge has remained intact. Medical knowledge, for instance. Chemotherapy, and plenty of advanced medical techniques have survived, albeit most of them are not widely available. I'm going to say no to making your own chemo-secreting organ, because even if it were possible without a very good working knowledge of biochemistry, such a thing would kill a lot of possible plot tension. [/hider]

In short, it's an interesting idea when taken to down to something thats less than perfect. You're trying to justify a wide variety of powers with only one. Not inherently objectionable, but you will have to scale it back a little, on all counts. You wouldn't be invincible, merely hard to kill. Not incredibly strong, merely quite powerful. Not mundivorous, but with a very wide apetite. Perhaps you've already addressed some of these limits. 

I just want you to convince me that you won't be no-selling anything that gets thrown at you. I'll reserve final judgement to when I see your CS.