I like the way in which this question points towards the way in which skilled writers leave no words unused. What can seem like incidental details are actually woven into the plot and theme of such fiction, and part of our appreciation of such texts is increased by the way that we have been tricked into believing that part of the text is not really significant, whilst in reality it is highly significant.
One example of foreshadowing that comes at the beginning of the story refers to the use of the Misfit by the grandmother to try and persuade her son to get him to take her and his family on holiday to Tennessee:
"Here this fellow that calls himself The Misfit is aloose from the Federal Pen and headed toward Florida and you read here what it says he did to these people. Just you read it. I wouldn't take my children in any direction with a criminal like that aloose in it. I couldn't answer to my conscience if I did."
Of course, ironically, this text foreshadows the fate of the grandmother and her family as they run straight into the Misfit, who treats them just like he treated the other people that she urges her son to read about. Note the way too that the grandmother is described as they set out on their holiday. Her elaborate attire is chosen with the sole purpose of identifying her as a lady in case of her death:
In case of an accident, anyone seeing her dead on the highway would know at once that she was a lady.
Of course, this text foreshadows her own death, and the way that she will end up lying on a road dressed in her full glory. These are but two examples of foreshadowing in the text. Hopefully based on these examples, you will be able to re-read the story and find some more. Good luck!