If i were to live out of a backpack, and thumb around the states, what gear should i take?

I plan on traveling around the states, seeing all the landmarks and sights, and i plan on doing this by backpacking and hitchiking... I know from experience that to bring too little makes for a sad trip, but I also know that to bring too much makes for a sore body and mood.... So the real question is how much is enough, and what do i need?