There is absolutely no reason beyond Dean's desire to shake off any lingering that-was-almost-weird for them to be moving this early. They're both tired and could both use some more sleep.

"Cas!" Argh. "Come on! We'll get coffee on the way."

He grabs one of the duffels and hefts it, heading out to the car without really looking to see if Cas is following, just trusting that he ultimately will.