Praise be to Allaah.
Charity (sadaqah) given on behalf of the deceased will benefit him and its reward will reach him, according to the consensus of the Muslims.
Muslim (1630) narrated from Abu Hurayrah that a man said to the Prophet (peace and blessings of Allaah be upon him): “My father has died and left behind wealth, and he did not make a will. Will it be an expiation for him if I give in charity on his behalf?” He said, “Yes.”
Muslim also narrated (1004) from ‘Aa’ishah (may Allaah be pleased wth her) that a man said to the Prophet (peace and blessings of Allaah be upon him): “My mother died suddenly and I think that if she could have spoken she would have given in charity [i.e., left instructions that some of her estate be given in charity]. Will I have a reward if I spend in charity on her behalf?” He said, “Yes.”
Al-Nawawi (may Allaah have mercy on him) said:
This hadeeth indicates that it is permissible to give in charity on behalf of the deceased and that doing so is mustahabb, and that the reward for that will reach the deceased and benefit him or her; it will also benefit the one who gives the charity. There is consensus on all of that among the Muslims.
Feeding the poor is one of the acts of kindness and charity that was enjoined by the Prophet (peace and blessings of Allaah be upon him), especially providing iftaar to one who is fasting.
Also among the best things that you can do to benefit your father and honour him is to make du’aa’ for him. The Prophet (peace and blessings of Allaah be upon him) said: “When a man dies, all his good deeds come to an end except three: ongoing charity; beneficial knowledge; and a righteous son who will pray for him.” Narrated by Muslim, 1631.
So you should make a lot of du’aa’ for your father, during your prayer and at other times, asking Allaah to forgive him, and admit him to Paradise, and keep him away from Hell.
And Allaah knows best.