Harry doesn't have any money in Cold Days. He has to borrow a nickle from Molly. Between Cold Days and Skin Game, Harry's stuck on Demonreach. In the flashback chapter towards the end of Skin Game, Harry doesn't have any money to buy a sandwich and beer at Mac's. When he has to pay Grey, he doesn't even have a dollar.
So all this leads to the question, how did Harry buy hamburgers from Burger King and all those fireworks?