Garage sales are less common in the UK but I will see people selling things outside their houses occasionally. What is more common here is Carboot Sales, where people will rent a patch of a carpark for a day and sell their unwanted thing there. It can be a great way to spend a morning as you never know what you will come across.
You can also donate directly to charity or to a charity shop which sells the clothes and donates the proceeds to the charity it represents.