Sal places a piece of pizza in front of Buggin' Out before they have their argument. After the argument, Buggin' Out sits down to eat his pizza. The piece of pizza looks different than the one Sal gave him.
Right before Sal begins to bash the radio, you can see Radio Raheem's arms on the radio as if he's leaning on it. The second Sal starts to bash the radio, you can see that Radio Raheem is standing a few feet behind the counter.
When Mookie throws the trash can through Sal's window, the reverse shot from inside the restaurant reveals the main camera, in the lower left portion of the screen, dollying in towards the window as it's smashed.
When Buggin Out is bumped into by the man with the bike, he gets hit on his left side, but when he looks at his sneaker, the scuff mark is on the outside of his right shoe. This is to further illustrate the mentality of these characters. They will look for a fight in any scenario and they are not concerned if their actions are justified. The man in the Larry Bird jersey didn't really scuff up Buggin' Out's shoe, but Buggin' Out was just such a loose cannon that he was waiting to be set off.
The goof item below may give away important plot points.
In the final scene, when Sal throws $500 to Mookie, he throws five bills, and Mookie throws two back at him. When Mookie goes to pick the money up again, he picks up two bills, but two more are visible in the frame, lying on the ground.