What to keep?

We are in the process of ridding our house of everything and anything that we don't use. This is always a challenge because there are so many things lying around that I intend to use but just never get around to using. For instance I have a drawer full of various imprinted promotional products I have been given at different conventions and conferences. So many of these things would be handy to have out on my desk if I just had more room for them. It is hard to know what to keep and what to purge. I guess we have to weight the cost of putting stuff in a storage locker versus replacing them when the time comes.