The most important thing would be to eat/drink something every two hours. You can indulge in things like smoothies, shakes, mashed potato, even well done pasta. Also things like broken wheat porridge, semi mashed khichdi, suji kheer are great options for the main meals. The trick is to make the meals nutrient dense. Add almond paste or blanched dates to your shakes and smoothies, vegetable purées to the khichdi.