It's so exciting that you will soon be seeing your grandson and that you will have the opportunity to get to know him. Like all kids, Casey may be fearful at first in a new environment and around new people, or people he hasn't seen in a very long time. It is important for you to learn what you can about autism, but also keep in mind the individuality of your grandson.
Understanding autism can help you in providing the patience and understanding that he will need as you get to know each other. Understanding your grandson will involve more than just an understanding of autism because no two people are alike; they may share a diagnosis but personalities vary all along the entire human spectrum.
Your grandson's parents can probably be most helpful and will appreciate you asking them what will make their son most comfortable while at your house. You can ask about specific foods, and activities or things that he may need to have around him to begin to feel comfortable. New things must often be added slowly and it helps to have familiar things for children particularly those on the autism spectrum for whom change can be especially difficult. As you become more comfortable with each other you will probably develop unique ways of being together that are comfortable for you to share.
From Bob Naseef:
It is heart-warming to hear from you about your grandson. So many parents of children who are diagnosed on the autism spectrum wish their parents would seek out information and support such as you are doing right now.
Your job is certainly complicated by the distance you live from your son and his family. That makes your job of getting to know your grandson as well as supporting your son and daughter (in law) more challenging. From what you wrote, I sense that you and your wife are up for it. Ask them where to start and how you can be a good parent to them and grandparent to their child. Speak from your heart and chances are excellent that their hearts will welcome yours.
Robert Naseef, Ph.D., and Cindy Ariel, Ph.D., are the co-editors of "Voices from the Spectrum: Parents, Grandparents, Siblings, People with Autism, and Professionals Share Their Wisdom" (2006). On the web at http://www.autism.about.com