Roger I am very sorry to hear about your cancer.
The best foods to add calories are nuts and seeds and nut butters, beans, avocados, wild rice, buckwheat, quinoa, oats, fatty fish like salmon, organic virgin coconut oil, extra virgin olive oil, and raw cocao beans. All of these are very nutritious and calorie dense.
I do not recommend any dairy, red meat or pork. If you are going to eat yogurt use goat or almond yogurt. I recommend unsweetened almond milk.
I hope this helps
Wally Bishop C.N.C.