Potatoes: Any form of form, be it French fries, plain slated chips, Aloo Tikki, Aloo Bhajiya or Aloo Khichdi, you can eat everything that is made from potato. However, it should not have any garlic, ginger, onion, red chilly powder, turmeric powder or coriander powder. Just sprinkle some rock salt on it and you are good to go. And if you have a sweet tooth, you can try making sweet potato halwa too!
Sabudana, Raagi, Rajgira, etc: Millets are considered the best types of foods during the fasting days. They give you the right amount of energy and are perfect for fasting. That is why you must have seen a lot of people eating Sabudana khichdi during their vrat. Similarly, you can replace wheat rotis with Raagi or Singhara rotis.