Harry's assets:

• Glasses - probably a distraction, but could be just about any nonhuman object, transfigured.
• Cedric - probably in the mokeskin pouch, not easily accessible, probably only useful as a human shield, which is not Harry's style
• Invisibility cloak - might be able to block the Killing Curse, useful in general, Harry is the Master of this Deathly Hallow, it's plausible but unlikely that he'd be able to Call it without words or gestures.
• Voldemort's bargain - Voldemort has promised in Parseltongue to protect one person for each power Voldemort knows not that Harry names.
• Partial transfiguration - both a Power Voldemort Knows Not and a tactical tool
• Wand
• Harry's own flesh (which he can use for partial transfiguration)
• The air
• The death eaters (including their robes, their bones, etc.)
• Sirius ("Mr Grim")
• Stuporfy

Foreshadowing / prior hints of resources:

• Thick/heavy enough physical objects can block curses aside from the Killing Curse
• Resonance between Harry's and Voldemort's magic more likely to harm/incapacitate Voldemort than Harry
• Harry was instructed by Voldemort to cast Mahasu on any student in the classroom, chose himself. Foreshadows choosing to use promise of protection on himself?
• Antimatter was mentioned earlier, Voldemort may not know enough about it yet.
• Hermione transfigures a Buckytube
• Use of Muggle devices
• Harry's prior weakness is that he doesn't ask others for help
• Harry decided to accept the idea that the air can't be transfigured before he figured out the insight necessary to do partial transfiguration, this could be wrong, the air as well as his flesh could be transfigurable
• Prophecy about tearing apart the very stars (meaning Sirius and Bellatrix and Draco?)

Harry had to remove his left shoe, and take off the toe-ring that was his emergency portkey if someone kidnapped him and took him outside the wards of Hogwarts (and didn't put up anti-Apparition, anti-portkey, anti-phoenix, and anti-time-looping wards, which Severus had warned Harry that any inner-circle Death Eater would certainly do).

That seems to rule out apparition, portkeys, phoenixes, and time looping, so transfiguring a time turner into his hands is out, as is trying to get into a Phoenix frame of mind to summon Fawkes or another phoenix to send a message, or using his portkey.

"There are desks which are heavy enough to be fatal if dropped from a great height. There are chairs with metal legs that could impale someone if driven hard enough. The air in this classroom would be deadly by its absence, since people die in vacuum, and it can serve as a carrier for poison gases."

Harry had to stop briefly for breath, and into that pause Professor Quirrell said:

"That's three. You need ten. The rest of the class thinks that you've already used up the whole contents of the classroom."

"Ha! The floor can be removed to create a spike pit to fall into, the ceiling can be collapsed on someone, the walls can serve as raw material for Transfiguration into any number of deadly things - knives, say."

"That's six. But surely you're scraping the bottom of the barrel now?"

"I haven't even started! Just look at all the people! Having a Gryffindor attack the enemy is an ordinary use, of course -"

"I will not count that one."

"- but their blood can also be used to drown someone. Ravenclaws are known for their brains, but their internal organs could be sold on the black market for enough money to hire an assassin. Slytherins aren't just useful as assassins, they can also be thrown at sufficient velocity to crush an enemy. And Hufflepuffs, in addition to being hard workers, also contain bones that can be removed, sharpened, and used to stab someone."

By now the rest of the class was staring at Harry in some horror. Even the Slytherins looked shocked.

"That's ten, though I'm being generous in counting the Ravenclaw one. Now, for extra credit, one Quirrell point for each use of objects in this room which you have not yet named." Professor Quirrell favored Harry with a companionable smile. "The rest of your class thinks you are in trouble now, since you've named everything except the targets and you have no idea what may be done with those."

"Bah! I've named all the people, but not my robes, which can be used to suffocate an enemy if wrapped around their head enough times, or Hermione Granger's robes, which can be torn into strips and tied into a rope and used to hang someone, or Draco Malfoy's robes, which can be used to start a fire -"

"Three points," said Professor Quirrell, "no more clothing now."

"My wand can be pushed into an enemy's brain through their eye socket" and someone made a horrified, strangling sound.

"Four points, no more wands."

"My wristwatch could suffocate someone if jammed down their throat -"

"Five points, and enough."

"Hmph," Harry said. "Ten Quirrell points to one House point, right? You should have let me keep going until I'd won the House Cup, I haven't even started yet on the unaccustomed uses of everything I've got in my pockets" or the mokeskin pouch itself and he couldn't talk about the Time-Turner or the invisibility cloak but there had to be something he could say about those red spheres...

This vaguely suggests a few options:

• Harry could improvise a dark ritual to sacrifice some of his internal organs to "hire an assassin" (counting on some sort of magical healing afterwards).
• Susan Bones might also be in the pouch ("Hufflepuff [...] Bones"). Note that the real Susan Bones was not with the other students who encountered Snape in the corridor.
• Harry likely knows of some efficient poisonous gases, if he can hold his breath for long enough he can simply transfigure part of himself into one of these and wait for the Death Eaters to drop.
• Harry could somehow try to cast a spell on Voldemort to invoke the resonance, push him in a direction that disrupts the semicircle of Death Eaters.
• Harry could transfigure the air around him into a thick physical barrier that blocks everything except the Killing Curse.

Ignoring the gasps rising from behind him, Harry crossed the radius of the Patronuses, strode to a single pace from Death. Its unhindered fear burst around him like a whirlpool, like stepping next to the sucking drain of some huge bathtub emptying out its water; but with the false Patronuses no longer obscuring the level on which they interacted, Harry could reach the Dementor even as it could reach him. Harry looked straight into the pulling vacuum and -

the Earth among the stars

all his triumph at saving Hermione

someday the reality of which you are a shadow will cease to exist

Harry took all the silver emotion that fueled his Patronus Charm and shoved it at the Dementor; and expected Death's shadow to flee from him -

• and as Harry did that, he flung his hands up and shouted "BOO!"

The void retreated sharply away from Harry until it came up against the dark stone behind.

Harry can sort of wandlessly wordlessly cast something like a Patronus, he could try to do something like this to Voldemort.

Beneath the moonlight glints a tiny fragment of silver, a fraction of a line... (black robes, falling) ...blood spills out in litres, and someone screams a word.

This strongly suggests a Buckytube monofilament whipped around to decapitate all the Death Eaters. This is the most plausible solution, and it's somewhat compatible with the other Partial Transfiguration option, which is to tell Voldemort about it in exchange for protecting Harry's life (and to buy time). This is also compatible with Harry's glasses being a transfigured shield (or transfigured charmed magical shield, in either case there's no reason someone couldn't have just magically LASIK-ed his vision), which would give him a defense against any non-Killing Curse spells that go his way from anyone he doesn't immediately kill. Then he lunges for (or accios) the pouch and cloak, retrieving Hufflepuff (Susan) Bones and Cedric, to help him fight the remaining Death Eaters (or go for help). Then he casts a Patronus to get McGonagall (and insists she not disrupt the game).

Ah, better yet - the glasses should be his broomstick. Or his broomstick AND a shield. AND a gas mask. Fit together (since glasses are composite objects anyway).

OK, so here's the attack plan, to tear apart Voldemort's plan at every possible point of intervention:

1) While transfiguring a long buckytube monofilament out of his own flesh, tell Voldemort about partial transfiguration, demand that Harry himself be saved in return.

2) Wordlessly cast the Patronus at Voldemort to try to throw him off balance - as a bonus, if he manages a worldess wandless corporeal Patronus it can do step 5 early, OR possibly block a Killing Curse (not sure).

3) Whip the buckytube around to slice through a bunch of Death Eaters. Simultaneously, wordlessly wandlessly finite incantatem the glasses to detransfigure his broomstick.

4) Fly to (or accio while dodging curses) the pouch, extract Susan and Cedric, put on the cloak. They know from battle class that they should lift the sleep spell on their ally Hermione. (Harry shouldn't since it would be an interaction with Voldemort's magic that would be more likely to harm Harry than Voldemort.)

5) Cast a Patronus to get help from McGonagall (who can use her time turner so as not to disrupt the game), telling her to bring every competent battle mage she can get.

6) Cast Stuporfy at Voldemort to try and trigger the magical resonance, then fly straight at him to give him a hug.