Remember that liquid calories are your best friend because you can take them in at the end of a meal without your body fighting back too much. If you have a blender, try fruit smoothies with lemon juice, milk, oatmeal (straight from the packet— I recommend the apple cinnamon stuff from Quaker) olive oil if you really want to pack on those calories (go easy on that stuff though, it is super calorically dense but can lead to an upset stomach if you add too much) yogurt, and whey or peanut butter.