You said, "See, look, that's yours!
Stacked on top with your brother's
See how the resemble one another
Even in their plastic little covers"

from Bon Iver – Blood Bank Lyrics on Rap Genius

Meaning

Deep in his soul he knew they were long lost relatives like somehow they just fit together in an unusually necessary way.
They can a resemblance between them by the labels on their blood donation packs.

To help improve the meaning of these lyrics, visit “Blood Bank” by Bon Iver Lyrics and leave a comment on the lyrics box