The Cleveland Clinic's oncology dietician recommended Carnation Breakfast VHC. It is like Ensure except it has 560 calories in a single 8 oz serving. I add chocolate powder to the vanilla drink (the only option). This was often the only food my husband could get down in the 2-3 days immediatlely following chemo.
You will not find this supplement on the shelf at your local drug or grocery store. Ask the pharmacy to order it for you, ours did not know it existed until I asked for it. It costs about $24.00/case at Walgreens.