In "To Kill a Mockingbird" Scout thinks of earlier times while awaiting the verdict. What are they and how do they tie to the themes?

This is actually a very interesting question.  Scout's mind does wander a bit while they are awaiting the verdict, but it doesn't wander without cause or purpose.  She thinks of things that tie very well into what is happening in the courthouse.  One of the first things that she thinks of is the afternoon that the old, rabid dog, Tim Johnson was walking down their street.  She says that the atmosphere that day is the same as it is now in the courtroom.  They all are just tense, watching and waiting, seeing what would happen.  They knew something bad would happen, they just didn't know what or in what form.  Of that day, Scout says, "Nothing is more deadly than a deserted, waiting street."  Scout feels the same way waiting for the jury to come in.  She says,

"The feeling in the courtroom grew until the atmosphere in the courtroom was exactly the same as a cold February morning...a deserted, waiting, empty street."

She compares everyone just waiting to see what the dangerous dog would to, to everyone just waiting for what the jury would do.  It is a subtle foreshadowing of the negative verdict that was about to be announced; the dog situation didn't end well, and neither did the case, and Scout's emotional radar picked up on that very insightfully.  This goes well with the theme of the mockingbird, that someone innocent is harmed.  We all want Tom to be found innocent so badly, but we suspect it isn't going to happen.  The novel's theme of prejudice and racism is emphasized as the jury comes back with a guilty verdict.

I hope that helps a bit; good luck!