This isn’t actually checkered, but it’s an olive green version of Sam’s Checkered Grey Plaid (which I named because I thought it was blue, and I've run out of names for Blue plaids). It’s standard cut and does up with buttons, not snaps.
In All in the Family (11x21), Sam wears this shirt the next morning after they arrive back to the Bunker with Chuck, and he and Dean talk about what it’s like having God in the house.
In The Thing (13x17), Sam wears this shirt at the end of the episode when he and Dean return to the Bunker to discover Ketch is there with Gabriel.
In Bring ‘Em Back Alive (13x18), Sam continues to wear this shirt for the entire episode.