I have a bag in my car today to drop off at our local consignment shop. Not only do they take clothes, but also household items. I love the ease of dropping things off vs. managing shop inventory. No price tagging, inventory lists or arranging of the goods. I just pick up a check every month.
There is always a bag in my closet to put in things I no longer want or need. This makes it easier to get rid of stuff - to always have a bag ready. I also always have a box open to put in stuff for charity pick ups.
I believe that the practice of having an open bag and an open box are invaluable to getting rid of stuff. They willing swallow my sacrifices of things - and give me back more space in my life.