Several charity organizations have large containers placed at several locations where one can dump the package of clothes or other items. One of them used to be at gate no 4 at Villaggio but I am not sure if it is still there. There was another one just in front of Qatar Charity office on Shahrah Muaither commonly called Shahrah Tejari. However, if the quantity is much, some charity organizations may even arrange to have the items collected from your place if you communicate with them.