Harry’s blatant enthusiasm when he says “Not at all!” after Ron asks “Do you mind? Everywhere else is full.”
Harry’s obvious thrill at being able to pull out a hand full of galleons and buy more candy than he’s ever been allowed to have in his life.
Harry’s absolute joy over sharing that candy with a peer, and potentially making a friend, something he’s never really had before.
Just Harry having something to be happy about for once, and not worrying that if he smiles too hard or laughs too loud or is caught having things, he’ll get locked up in the cupboard again.