The greatness of food charity is explained in numerous ways in Hindu religion. Here is a story from Mahabharata involving Karna which reveals the supremacy of food charity over other charities.
Towards the end of the Mahabharata war, though Karna was losing in the battle, he still remained invincible on account of the merits of his charity. Bhagavan Sri Krishna, in order to deplete this source of strength of punya or merit, assuming the guise of a Brahmin approached Karna for charity.
Karna pleaded helplessness as he had nothing more with him to give except his life which he was ready to offer at the feet of the Brahmin.
Bhagavan Sri Krishna in disguise said that he had no need for his life, but He asked him to donate all his Punya which alone travels with the soul after death and secures a place in Heaven. Karna acquiesced to this demand readily.
But before performing the formal act of charity, Karna said that he was tired and thirsty and wanted some water to drink. When the Brahmin poured water from his water-pot into Karna’s palms, the water turned into gold again and again. Karna was assailed by fatigue and thirst and asked desperately why the water was turning into gold.
Then the Brahmin asked Karna whether he had given any food in charity during his lifetime. Karna said that he had always donated only gold, jewelry and such precious treasures. The Brahmin replied that he was therefore not destined to get any item of food or drink, as there was no such merit in his store to draw from.
Suddenly, Karna remembered an incident. When a Brahmin came to him for food, he had directed him with his index finger to Yudhisthira who was distributing food. On hearing this, Bhagavan in disguise told him to suck at his index finger. When Karna did this, a tiny spout of water sprang from that finger, by which his thirst was quenched. Thereafter, in a ritualistic way, he poured water and donated all his Punya. Bhagavan then revealed His true form which delighted Karna’s heart.