In American Gods by Neil Gaiman, what is the significance of Wednesday getting mead for Shadow at the bar?

Wednesday's action of getting mead for Shadow is significant because the drink is  symbolic of who and what Wednesday represents.
Shadow later discovers that Wednesday is an incarnation of Odin, the god of war, knowledge, poetry, and death. In Norse mythology, mead was the drink of warriors and gods. Accordingly, two warring factions of gods made peace by collectively spitting into a cauldron, effectively birthing a special being named Kvasir. Kvasir was later murdered by the dwarves Fjalar and Galar. The two mixed Kvasir's blood with honey to create the "mead of poetry." This mead was supposed to bequeath wisdom to all who drank it.
Odin was said to have later obtained this potent mead. The Norse warriors drank mead during important occasions; it was a drink that sealed the bonds of camaraderie and loyalty.
In the story, Wednesday makes Shadow drink mead three times.
The drinking of the mead seals the bargain between Shadow and Wednesday. Shadow is to protect his new employer, run errands for him, and transport him to wherever he wishes to go. When the situation calls for it, Shadow is also supposed to "hurt people who need to be hurt." In return, Wednesday promises to make sure that Shadow's needs are adequately provided for.
So, Wednesday's action of getting mead for Shadow is significant in that the drink symbolizes who and what Wednesday represents: an incarnation of the god Odin, who will lead the Old Gods into battle against the new American Gods.