Not every blanket is a good choice. You need something that is lightweight and dries quickly. I looked around my house for all of my blankets and found plenty for each member(including the dog:)
Poncho: It is a great idea to have a poncho in your pack to keep warm and dry. Wish I had one this week...Also about a dollar each.
Do what works best for your family!
(It's time to Plan Not Panic by Barbara Salsbury)