This is kind of a mystery at this point in the novel, but an attentive reader will think that it must have been Boo Radley who put the blanket around Scout's shoulders. All of the other people who lived on their street were "accounted for" in regards to their actions that night. At this point in the novel we aren't exactly sure what to make of Boo Radley, but the rumors the child relates are scary and the children play games of dare in regards to him and his house, but we also know that he was trying to reach out to the children in a kind way through the presents left in the knot hole of the tree and that eventually he will stop Bob Ewell from his attack on the kids. In the very last chapter of the novel, as Scout stands on his porch and "in his shoes" she sees that Boo Radley was always attentive to and concerned for the kids. It makes sense then that he would be the one to notice a shivering, scared Scout on the street the night of the fire and bring her a blanket.
Boo Radley. In Chapter 8, Miss. Maudie's house catches on fire. Jem and Scout are ordered to stay put in front of the Radley's house. It is a cold winter's night and the children aren't quite dressed for the weather. While shivering and watching the fire, hypnotized by the licking flames, Boo Radley sneaks up and covers Scout's Shoulders with a brown wool blanket. Imagine, after all the kids have gone through trying to see this, mystery man, he is less than 2 cm away from them, right out in the open. It makes me Laugh Out Loud:D