Śrī Caitanya Mahāprabhu said, "I will not be able to eat so much food, and it is not the duty of a sannyāsī to leave remnants."
According to Śrīmad-Bhāgavatam (11.18.19):
bahir jalāśayaṁ gatvātatopaspṛśya vāg-yataḥvibhajya pāvitaṁ śeṣaṁbhuñjītāśeṣam āhṛtam
"A sannyāsī should take whatever edibles he gets from a householder's house, outside near some lake or river, and after offering the food to Viṣṇu, Brahmā and the sun (three divisions), he should eat the entire offering and not leave anything for others to eat."