What does Odysseus talk about his gifts? How is this foreshadowing?

When Odysseus and his men find Polyphemus's cave, the crew just wants to take some food and go, but Odysseus refuses.  Instead, he wants to stick around until the Cyclops returns home in the hopes that Polyphemus will offer Odysseus a gift.  Odysseus might expect a gift because of the Greek notion of hospitality.  They believed that Zeus protected travelers, and so everyone had a responsibility to be hospitable, and this often included the host giving the guest some kind of a gift.  This is why Odysseus would speak of gifts here.

One way in which his speech foreshadows what is going to happen is that Odysseus says that, rather than refusing his crew's request, it would have been "far better had I yielded [...]."  This lets us know that the outcome of his decision is negative because he would, knowing what he knows now, have wished to avoid it.  Before he even tells us the story of the men's time there, he says that it would have been better for him to have taken his crew's advice.