Nothing.
Boo Radley gave the blanket to Scout when Ms. Maudie's house caught on fire.
Scout comes home with a rolled piece of gum that she found in the knothole of the tree at the Radley place. It is believed that the gum is left by Boo Radley.
Boo Radley
Boo Radley covers Scout with a blanket near the end of "To Kill a Mockingbird" after she witnesses an attack on her and Jem by Bob Ewell. Boo intervenes, saving them from further harm, and then carries the injured Jem back to their house before covering Scout with a blanket. It is a significant moment that shows Boo's protective and caring nature, revealing his true character to Scout and the readers.
Boo Radley.
a blanket
Boo Radley. He silently places it on Scout, because of the coolness, while she and Jem were watching the fire. Scout and Jem were so indulged by the fire consuming the town that neither noticed when the blanket was wrapped around them.
Though the book does not actually say who put the blanket around Scout, we as the reader are made to think that it was Boo Radley. Boo may have not known that Scout was cold at all, and just did it as a sign of caring friendship and to emphasise the idea that Boo Radley is there for her and Jem.
Scout gets the blanket on the night of the fire when someone kindly wraps it around her shoulders while they are evacuated from their burning home. Scout is unaware of who placed the blanket on her, but later learns it was Boo Radley who saved her life during the fire.
Jem realizes that Boo Radley must have been the one to cover Scout with the blanket during the fire, showing that he had been looking out for them all along. This revelation deepens Jem's understanding of Boo's kindness and concern for their well-being.
The blanket that Boo Radley put around her
Boo Radley put the blanket around Scout in Chapter 8.