Nub prays to Venkelvore, Hadragesh's consort, who's hunger causes Her to steal food even from the other Hero-Gods. She teaches Goblins to be always hungry, that enough is never enough. She got him into this situation, didn't She? Maybe She can get him out of it, too.

You've had a surplus of available food for months now. If you'd just produced a few dozen children already, evolutionarily speaking it wouldn't matter that you're about to die.

But I wanted more food and stuff?

Wanting more food and stuff is for people who've saturated their ecosystems local carrying capacity. Breed more, then come back to Me about feeling hungry.

Nub prays to Zarongel the Bark Breaker, who taught goblins how to kill dogs, and who has fire for hair as a gift from Lamashtu that Nub doesn't really understand at all. Does He have any advice?

Buddy, just try your best to kill the dragon. It's not totally impossible. Even if you can't do it, at least give it your best shot. With enough Goblins one of you will figure out a way that works eventually, and then he can tell the rest.

Nub prays to Zogmugot, Lady Lastbreath, who is goddess of scavenging and flotsam and drowning, who tricks the unclever with shiny things and then drowns them in the sea if they displease Her.

Why not just grab all the valuables while they're still in reach and take your chances in the Astral? You've only got a couple rounds left either way.

No help at all, figures.

Nub is going to try to do every useful think he still can while inside the bag, and then if nothing happens until right before he's about to pass out he'll try to cut it open and see what happens after that.

A few thousand feet in the air, and a few miles south of where those adventurers last saw him, Dergaix stop flying, and pulls Nub out of the bag.

Retrieving a specific item from a bag of holding is a move action, unless the bag contains more than an ordinary backpack would hold, in which case retrieving a specific item is a full-round action.

Nub's not an item, he's a creature. Rules as Written, there's no way to take a creature out of a Bag of Holding.

Then Dergaix turns the entire bag inside-out.

Do the contents all fly apart in random directions?

The canvas sheet of a camping tent is tied into a bundle around the adventurers spare clothes, scrolls, the Aurochs horns and meat, Nub's rabbits, and a few rocks that Nub thought were shiny.

The other end of the rope is around Nub's waist, along with the coin purse and a small bag of every potion and useful alchemical item Nub could find in the Bag of Holding.

They are 4600 feet in the air. They will fall 500 feet in the first round, and 1500 feet in each subsequent round.

Dergaix would like to attempt a DC 20 Fly check to stylishly fall at the same speed as Nub, and thereby remain only a short distance away from him.

1d20 + 14 = 33.

Dergaix is more aerodynamic than a flailing Goblin.
If he wants to stay nearby he can do that.

Dergaix would like to use his breath weapon.

2d10 fire damage, DC 15 to half?

Nub has a +3 Base Reflex Save (Rogue 2)
Nub has a +5 Dexterity bonus (20 Dexterity)
Nub still isn't wearing any armour.
Nub has +8 to Reflex saves.
1d20 + 8 = 20.

Nub passes, and can take half damage.
Nub drank a potion of Resist Energy (fire) while he was inside the backpack.

2d10 / 2 - 10 = - 3.
Nub is fine.

Nub would like to attempt, in order, a DC 30 Linguistics check to express a desire to submit to this dragons will via Interpretive Dance, a DC 20 Acrobatics check to perform said Interpretive Dance while in freefall, and an opposed Bluff check to be believed about it because even now he would still in fact be lying.

Linguistics is a Trained-Only Skill.

It might be a class skill for Rogues, but you still have to actually put a rank into it at some point. You never learnt any Linguistics, so you're not allowed to even attempt the check.

Nevermind then. Nub would like to grab the Bag of Holding, climb into it, and then stab it from the inside. He doesn't like being here any more and would rather take his chances on the Astral.

It's not within reach. Dergaix is still holding it in his back claw.

Can Nub stab the Dragon?

Dergaix recently learnt the advance technique of staying within reach of his Breath Weapon but out of reach of melee attacks. He's hoping to try it out on a different opponent in a new setting, to see how general the strategy is.

As long as you don't grow wings and he keeps passing his Fly checks, no, you can't.

Can Nub shoot the dragon with a poisoned arrow?

Sure. He's only 15 feet away.
Nub has a +1 Base Attack Bonus (Rogue 2).
Nub has a +5 Dexterity Bonus (20 Dexterity).
Nub has a +1 Size Modifier (Small).
Nub suffers no range penalty.

Nub has a +7 To hit. Dergaix has an AC of 19.
There is a 40% chance to hit, in which case you can deal 1d4 damage.
You will average 1 damage / round, killing Dergaix in approximately 6 minutes.

As for poisons, he has a +7 to saves, and your best options are mostly DC 11 and would take at least 3 effects to incapacitate him if you get lucky.

Also you have approximately 3 rounds before you hit the ground.