What are the materials should be discarded each month in this 4 month vrata period? Like dal,cumins,milk, curd etc, Vegetable, fruits.
Chaturmas’ is the period of four months from Ashadh Shukla Ekadashi (Eleventh day of the bright fortnight of the Hindu lunar month of Ashadh) to Kartik Shukla Ekadashi (Eleventh day of the bright fortnight of the Hindu lunar month of Kartik) or Ashadh Pournima (Full-moon day) to Kartik Pournima.
This four months period in a year is assigned for penance, austerities, fasting, bathing in holy rivers and religious observances for all. Devotees observe some form of vow, be it of silence or not eating a favourite food item, or taking only a single meal a day.
During this period Deities or Gods take sleep or Mahanidra.So it's believed that demons become active during this time. The scriptures say that, ‘to protect oneself from these demons each one should undertake some vrat (Vowed religious observance).
वार्षिकांश्चतुरो मासान् वाहयेत् केनचिन्नरः ।
व्रतेन न चेदाप्नोति किल्मिषं वत्सरोद्भवम् ।।
Meaning : Every year during chaturmas, we should undertake some vrat otherwise we will incur the sin of samvatsarodbhav.
Comming to your question , what materials is to be avoided is i think pretty personal question and may vary from region to region .But according to beliefs.
According to popular belief...
Devotee,s avoide certain food iteams. e.g. Salty foods, Spicy foods, In some regions devotees avoide certain food iteams during each months.
In Shravan Month they avoid leafy vegetables , Non-Vegetarian food etc.
During Bhadrapada Month curd is avoided.
In Ashwin Month Milk is avoided.
In Kartik Month Dal, Pulses are avoided.