One of the most important things you can do to support your dog is to provide the most natural, highest quality nutrition possible. Food, after all, is the foundation of all health. Dr. Dressler generally recommends a home-cooked diet for dogs with cancer, and if commercial dog food is used, your dog will benefit most from a high-quality brand.
It may seem more expensive, but you will get more value per mouthful than with lower quality, cheaper brands. Most of the food he recommends in The Dog Cancer Survival Guide is best bought fresh in your local store, but you'll find a few items on this page that may not be otherwise available in your area.