Well then...typically, electronics have trace ammounts of gold in their circuitry (VERY little though), and I think you could make a justifiable case for having it drop plastic bars upon being processed. There should also be iron/steel, and maybe aluminium; you'd have to get someone who knows alot more about vehicles than i do (if nuclear powered though, you could also give them the potential to drop pitchblende/uranium bars-or have the processing of the corpse a chance to cause an explosion).
One big issue though is the idea of adamantium still being in the game. I would like to suggest replacing it with something else-i recommend a "unkown alloy" (the idea being it was a secret alloy developed either by the governments before their downfall, or the military shortly thereafter). This wouldn;t be as strong as adamantium is nor as light (though still light compared to say, iron), but it would beat anything else you have to work with. Now, what could be sealed in the vaults? Gold bars? A seed bank for emergencies? Everything in fort Knox?
And the answer should not be the HFS we all know and love. They're too frail and sheltered for this world-well, the japanese hentai monsters might not mind it. Regardless...HFS, revamped! No raws yet, but I might be able to make them *some* time... really busy atm though.
Gigas: The bulky, fast, brutal result of whatever created the infected, this thing is ten times worse than the worst tank you'll ever meet. Big as a colossi, heals about as fast, and intelligent enough to open doors. Can destroy anything it comes across with ease-and has an extra pair of arms to do it with. Maybe even an extra pair of legs, if you get unlucky. Very tough to take down, but since they're so big there aren't quite as many of them.
Ghouls: Innumerable, ravening hordes spill forth. Faster than the average infected, much, much faster. Smallest of these, not too much larger than the average infected...but if it gets too close, blink and you'll miss the carnage. These guys don't open doors, they just rip them down. Their mad lust for flesh is stronger than even a normal infected's, and will feast on anything that moves, leaving dozens of strewn chunks in their wake. They have six legs and only one pair of arms-but that one pair is all they'll ever need. You see now why there was a vault down there, don't you? Bet you wish you could seal them back in...or you would if you were still alive and not being digested. You better be able to kill them all very, very fast, or they will kill you.
Deadels (name a tribute to sluggy freelance): Lead the infected, and make even gigas look weak. Intelligent enough to open doors, powerful enough to rip Chuck Norris a new one, tough enough to take on ten tiles of 10 spikes in traps and just shrug it off. Only infected to still have partially functional organs apart from the digestive system. Can still speak, and gloat over their meals (keeping adv. mode in mind). Can jump so high they might as well just grow wings and fly-don't think a pit alone can stop them! Might as well remember there's no such thing as enough dakka, and pray.
Nightmares: These eldritch abominations may be what brought the plague. Their horrific appearance alone is enough to paralyze one with terror-a head with 4 mouths, 13 tentacles, each with a mouth of their own on the end, no eyes, and no legs that floats above the ground, advancing silently-in our own dimension, at least-towards its prey. They radiate a constant stench of death and decay, but fortunately are easily located due to their ability to breathe a cone of flame over their victims. Unfortunately, this also makes them very deadly since they're also fast.
Reapers: These infected move silently with stealth, while the others do not (technically, nightmares aren't infected-maybe). Easily the smartest, they share the same weakness of springing themselves and feasting on anything that has a pulse. Carry weapons (if possible), and can end up in the middle of your camp before your realize what has happened (if the people involved have never encountered the HFS, at any rate). Sort of the glass cannon of the HFS-if you get lucky they aren't TOO bad...but if they slip past you, woe unto you.)