Where do we begin?

For several years, Carl and I have been talking about and "planning" to someday head out in Pegasus, our motorhome, and come back when we're darn good and ready.  Carl retired in 2014 and we took our first LONG expedition to Washington State, and I was hooked.  That was the first time I've ever seen much of these great United States.  I had planned to retire in 2017 and we have been planning to head to Alaska.  However, things have worked out so that I am going to be able to retire a year early ...  which means we put these plans on the fast track.  Needless to say, I am EXTREMELY excited and ready to get this show on the road. Where do we begin?  How do I pack all my STUFF for four months on the road?  What are the things/places we must see"?  Send us your thoughts and suggestions.  July will be here before we know it.  I wonder where we'll wander ...