It's time to have a rethink about the mindless consumerism which sees secondhand stores overloaded with donated goods, a large percentage of which they have to pay to send to landfill.
The Story of Stuff describes it beautifully in this video.
This article on the rise of the conscious consumer is an interesting read.
Reduce the accumulation of items by buying only what you really need, buy good quality and use with respect to ensure longevity of the item.
Whanganui has a great number of excellent secondhand/charity shops where you can donate clean items in good condition which you no longer need.
If your secondhand item is not reusable, check if all or part of it can be recycled.