Being or shopping in a charity shop generally means you like giving to others and enjoy the contentment life brings- your happiness isn't routed in material things.
Shops are usually about the choices you have in your life and if you couldn't find anything to buy, perhaps you feel you don't need anything else in your life right now- it's fine as it is. Or maybe you are struggling to find your next path but feel you need one.
When you buy something from a charity shop in a dream it often signifies the appreciation for what you have in your life but you may also like to give others help where you can in the hope that they will feel the same one day.
Another interpretation is that you might have been trying to convince someone else lately about the importance of giving things away. Perhaps something they don't use could be of value to another person and your aim was to get them to see that.
It can also be about recycling your parts of you- such as your feelings, skills and knowledge. Perhaps you think you are repeating these things over and over again to the point where you feel you need a change at home or in your professional life.
Tagged in Dream Interpretation