You will need a detailed listing of what you give, when you purchased it, what you paid for it, and what the fair market value was on the date of donation. You will also need a dated receipt with a description of what was donated from the charity you give it too. The receipt should also include the address of the charity and a statement to the effect that you received no goods or services n exchange for the donation. If any one item if worth more then $5000 it will need a separate official appraisal before the date of donation.
As a good practice I always tell my clients to take pictures of the items either immediately before donation (i.e. while they are being loaded up) or at the donation site.