"Here." Dean tosses him the slightly lumpy twinkie, and refuses to make eye contact. They didn't have cake at the gas station, which just happened to be the only civilization for miles. "Happy birthday."
Rod lets out a grunt of surprise around a mouthful of gas station nacho (garenteed to contain no actual meat, and arguably no cheese either!), tries and fails to catch Dean's eye. That's fine. The little snack cake feels too heavy on his thigh, and it takes him a couple moments to get back to eating anyway, without focusing on trying to talk around the sharp edges of gratitude in his mouth.
Rod has a car of his own, a shiny red muscle car that holds more guns than you'd think and gets him where he needs to be, and he's in Dean's car instead because neither of them like to be alone the ac is garbage. It's convenient, going in the same direction and doing the same kind of things. The car purrs and the radio howls and they keep going into the twilight; and Rod thinks about how if he said no one's given him a gift that wasn't a weapon since he was eight, Dean'd understand. (How he doesn't know what to do with his hands when he's not getting into trouble or trying to get someone into bed. How emotions get caught up with weakness, with being abandoned, and everything turns to knives in his mouth) He doesn't, of course.
Sometime around mile marker 69 (nice, ha), Roderick does reach out to turn the radio down; and that gets Dean to cut his eyes over long enough for an exaggerated wink and a laughing "Cream filling, huh?"