How was Smaug's treasure actually divided?

Yes, Bilbo gave up his 1/4th share to Bard, but I think after that both Dain & Bard gifted him a sack/chest which he carried back on his pony, plus he had the small treasure hoard of the Trolls, plus he was already rich to begin with. Baggins was a second-level Hobbit 'Aristocrat/Noble'Family, wealthy enough/'noble' enough to marry into the chiefly clans of Took & Brandybuck. He was landed gentry, a Gentleman 'Farmer' with enough land & tenant farmers that he didn''t need to work ...thus able to pursue his writing & translation work.

Dain was going to give Bilbo his 1/14 share even after the deal for the Arkenstone but Bilbo agreed only to two small chests (one filled with silver the other with gold) because Bilbo really didn’t care for the gold because it really had no use for him in his hobbit hole under the hill and was to much a burden to ever get back there.

I believe that Bilbo got the Troll's gold, which had been buried, on his way back home with Gandalf. This is perhaps what he means when he told his nephew Frodo that he only got "two small chests, hardly overfilling". I'd have to look at the book to be certain it is even mentioned, as the screenplay took advantage of the "literary license" (changes from the original screenplay and the books). Personally I suspect that he got much more somehow, on account on how rich he was for the long remainder of his life and him being generous until he went away on the ship.

I don't want to delete my old answer, but after reading all the comments and thinking about it while cycling to work. I think this is a more accurate answer.

As the Mathemagician pointed out, no agreement to give each dwarf an equal share was ever mentioned in the books. It does seem very unlikely that Thorin was going to divide up the hoard that was his fathers and his father's fathers into 14 equal parts. No doubt he intended to claim the hoard as his and reward his followers and friends as he felt they deserved.

The special agreement with Bilbo was drawn up to convince him to leave his comfortable home behind and come with them to the mountain. His share was to be "one fourteenth share of total profits, if any".

By this, no doubt they were thinking of any profits they made on the journey to the mountain (such as the pot of gold coins they took from the trolls, Bert, William and Tom) or anything that he might be able to steal from the dragon. Even Gandalf didn't think they would end up killing the dragon and claiming the entire hoard.

"that is why I settled on Burglary."

As Gandalf put it, it was a chance for Bilbo to make his fortune.

"Very amusing for me, very good for you - and profitable too"

When they drew up his contract, they were probably thinking: at the least they'll have to offer him a fair share of anything he burgles from under the nose of a dragon.

So 13/14 of the treasure was officially Dain's (as Thorins cousin and heir to the treasure) and it stayed in the mountain. From this, Dain no doubt paid every one of the surviving companions with wealth and titles.

Bilbo took the Arkenstone as his 1/14, gave it to Bard. Bard agreed to trade it to Thorin for the 14th share in gold (wrought and un-wrought) and Dain honored the agreement of the dead.

So, that's how the treasure got divided.

(Also is anyone else really excited to see how Billy Connelly portrays Dain in the upcoming movie?)

Ok, I'll replying to Brians comment in here, because there's so much more space:

I do agree Thorin considered the Arken Stone at much higher than 1/14, and was happy to write off 1/14th of his hoard to buy back the stone. He probably would have given over half of it, if it was the only way he could get the stone back.

Here's the quote about him choosing his reward:

“Now I am a burglar indeed!” thought he. “But I suppose I must tell the dwarves about it—some time. They did say I could pick and choose my own share; and I think I would choose this, if they took all the rest!”

Here are his last words at the Gate, which he took back later.

"I am betrayed!" It was rightly guessed that I could not forbear to redeem the Arkenstone, the treasure of my house. For it I will give one fourteenth share of the hoard in silver and gold, setting aside the gems; but that shall be accounted the promised share of this traitor, and with that reward he shall depart, and you can divide it as you will. He will get little enough, I doubt not. Take him, if you wish him to live; and no friendship of mine goes with him."

It looks like your answer contains all the detail that was in the story. All of the dwarves stayed in the lonely mountain so the bulk of the treasure stayed there.

Bard requested a share of the hoard because Smaug sacked Dale, including the emeralds of Girion, which the Elven king ended up with because he loved forest green gems so much.

I don't think there was any agreement to give 1/14th away, I imagine Dain handed out gifts and rewards to anyone who helped overthrow the Goblins.

There's no reference in the books, but I always imagined Dain offered Beorn rich rewards too which were turned down.

Also the logistics of counting the value of the entire hoard, balancing the value of gems vs gold and dividing it by 14 would have taken years anyway. Practically I'd say it was more a case of loading some wagons or donkeys with gold and silver cups and plates to redecorate the rebuilt halls of Dale.