Talk to a RailFan - you will learn a LOT about Trains.

If you are travelling from Delhi to Karnataka or beyond then, Before boarding the train from Hazrat Nizamuddin, purchase some light snacks like Biscuits, chips etc. This will definitely come handy next day morning if you somehow wake up after Kota. If you wake up before Kota departure, then you will get good breakfast at Kota station or else fill your tummy partially by those biscuits/chips. Majority of time it arrives Ratlam on time with minimal delays, so do a heavy breakfast here. Also purchase Thaali or some food items for Lunch from Ratlam station itself for cheaper cost. For dinner, you can depend upon Vasai road. Book online dinner from Vasai road by E-catering.
Next day breakfast is not much of...
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a problem as sufficient options you gonna get from Ratnagiri-Madgaon stretch. But after Madgaon till Mangalore, it gonna be a hard time finding good food. So, from madgaon itself, purchase ample food for further journey. Once you enter Kerala, No problem at all for food items.