[Child of the 7th Age]

What about Frodo's dreams as a clear foreshadowing of his departure to the Blessed lands, especially the one when he is at Tom Bombadil's house at the beginning of the quest?

That night they heard no noises. But either in his dreams or out of them, he could not tell which, Frodo heard a sweet singing running in his mind that seemed to come like a pale light behind a grey rain -curtain, and growing stronger to turn the veil all to glass and silver, until at last it was rolled back, and a far green country opened before him under a swift sunrise.

And another foreshadowing of the same that occurred in Rivendell after the Ring had been destroyed, when Sam was speaking with Frodo:

'Well, Mr. Frodo, we've been far and seen a deal, and yet I don't think we've found a better place than this [i.e. Rivendell]. There's something of everything here....'

'Yes, something of everything, Sam, except the Sea,' Frodo had answered; and he repeated it now to himself; 'Except the Sea.'

Also, the phial of Galadriel can be seen as a foreshadowing of what Frodo himself will become by the end of the book. You can see this possibility when Gandalf speculates earlier in Rivendell what might become of Frodo:

He is not half through yet, and to what end he will come not even Elrond can foretell. Not to evil, I think. He may become like a glass filled with a clear light for eyes to see that can.

Other references to light occur throughout the book in relation to Frodo which reinforce this foreshadowing, specifically the descriptions of him having the light of an Elf-friend in his eyes.

sharon