When Omar is walking through the alley you can see him carrying a double barrel sawed-off shotgun under his coat.
However, when he is robbing the stash house minutes later he is using a pump action 12 gauge shotgun.
The goof item below may give away important plot points.
In relation to Omar's death, the female writer at the Baltimore sun is going over with the editor which story of two should be included in the upcoming edition. She says one is the homicide of a "34 year old" male at a grocery store. At the very end of the episode, they open the body bag to reveal Omar's corpse with the wrong tag. On the tag for Omar it shows his birth date being "August 11, 1960". This would make him 47, not 34.