Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.088A.

Ibn al-Qayyim said, “The best present for the deceased is an act that is most beneficial to people, for example, freeing a slave. Thus a sadaqah giving in charity is better than fasting on behalf of the deceased. The best charity is that which fulfils someone’s need and is continuous. The Prophet, peace be upon him, said, “The best charity is to give people a drink of water.” This applies to a place where water is scarce. Otherwise, giving someone a drink of water from a river or a canal would not be better than feeding the hungry who need food. Likewise, supplication and asking forgiveness for the deceased is beneficial to the deceased, especially when the supplicant is sincere, earnest, and humble in his supplication. Such a supplication is better than charity, just as regular prayer (salah) is better than the funeral prayer and than supplicating for the deceased by his grave.

In general, the best gift to send the deceased is freeing a slave, giving in charity, asking forgiveness for him or her, and making the Hajj (pilgrimage) on his or her behalf.