A gold box signed by R.A.B
One reason is that he is Voldemort's horcrux. Only by destroying Voldemort's seven lockers can Voldemort be defeated. Another reason is that this is what Dumbledore and Hewlett-Packard are finally looking for, and it is their last memory. Hewlett-Packard also believes that if Dumbledore had not drunk the poison in the holiday locker basin, he would not have died.