I am not sure if there are any sources which give details related to the regulations on food for sanyaasis. If anyone knows some information in this regard either through direct experience or from other sources, please share.
Edit: I don't think we should club sanyaasis with yogis, in this context. I have told that there are a plethora of rules for a sanyaasi whereas the definition or the derivative rules for a 'yogi' are about as vague or diverse as they can be.
The most crucial thing for them is they have to beg for food. Since they have abandoned fire they are not allowed to cook for themselves. So, the only option left for them is to beg and secure food. That is the only method by which they are allowed to secure food.
And, for that purpose, some of them use a bowl (which they were presented with during renouncing) whereas some simply use their hands as bowl.
Let him then take nothing besides a loincloth. "Thereafter they live the life of mendicants. Celibacy, noninjury, non-possession, and truthfulness—guard these assiduously."
"Now, Paramahamsa renouncers sit and sleep on the ground. Celibates use bowls made of clay, bottle-gourd, or wood, while ascetics enter a village to beg for food, using their hands or stomachs as begging bowls.
Aruni Upanishad 12
The amount of food that is prescribed for them is usually just eight mouthfuls.
He may beg food from all four classes. He should take his food using his hand as a begging bowl, Let him partake of food as if it were medicine; and let him eat whatever he happens to get merely to sustain his life, so as not to put on fat and to remain lean. Let him spend just one night in a village and five nights in a town. He may spend the four months of the rainy season in a village or in a town
Kathasruti Upanishad 32-33
There are also restrictions regarding the number of houses he can beg from. This style of begging is called Madhukara Vritti (the style of the bees) ( taking little little amount of food from certain number of households).
"A Bahudaka wears a topknot, a patched garment, and so forth, as well as a triple mark on his forehead, being similar to a Kuticaka in all things. He eats eight mouthfuls begged in the manner of a bee. "A Hamsa has matted hair and wears a triple and a vertical mark on his forehead. He eats food begged in the manner of a bee from houses that he has not preselected, and he wears a rag as a loincloth.
Turning once again to the distinction among ascetics, a Kuticaka begs food from a single house. A Bahudaka begs in the manner of a bee from houses that he has not preselected [NpU 174, n. 59]. A Hamsa begs eight mouthfuls from eight houses. A Paramahamsa begs from five houses and uses his hand as a begging bowl. A Turiyatita eats fruits and uses his mouth in the manner of a cow . An Avadhuta obtains food from all classes in the manner of a python.
Narada Parivrajaka Upanishad
He obviously can not demand so he does not have any control over the kind of food he will receive.
Basically, he has to eat very moderately and also has to avoid consuming certain food items like Ghee specifically.
Let him beg food, avoiding those who are infamous or fallen from their caste, heretics, and temple priests. In times of distress he may beg from all classes. Ghee is like dog's urine, and honey is equal to liquor. Oil is pig's urine, and broth is equal to garlic. Bean cake and the like are cow's meat, and milk is equal to urine. With every effort, therefore, an ascetic should avoid ghee and the like. Let him never eat food mixed with ghee, broth, and the like.
Brihat Sannyasa Upanishad
