There are many tiffin items available at your disposal. Again depends on what kind of food would you prefer for your tiffin. There are sandwiches which would take minimal time for preparation and are very healthy and filling as well. Plus there are things like upma, khichdi, or say a vegetable gravy with some rotis or chapattis. The items mentioned other than the sandwiches take longer period of time to prepare, but not that long and thus are really easy to prepare. Other than that I can suggest you things like magi noodles and other instant food items available in the market.