Don’t know if you’re still doing this but if you are:
Hi Nonny! definitely ongoing :)
1—Harry replaces Ron’s wand in CoS.
Because McGonagall is not a dangerously negligent teacher, she noticed that Ron’s wand was dangerously faulty, and arranged for an appointment with Ollivander at the school (standard procedure after dire wand-eviscerating accidents), and sent a letter home informing Mr and Mrs Weasley of the necessity. Of course Ron’s parents come to the school, and of course Harry’s there in the common room when Ron is about to get dragged off to see Ollivander after classes are over, and of course he overhears a bit of the conversation outside the portrait hole about the expense of wands/money worries. And Harry, who is shown to have enough emotional intelligence to navigate situations like this all the way back on the train journey to Hogwarts in first year and I will die on this hill, and who spends so much time in the second book noticing Ron’s broken wand and feeling guilty about the car and the howler and the MoM fine and the trouble to Mr Weasley in a way that would very much appear to be leading somewhere, pulls a wait here a second! while he sprints upstairs to grab seven galleons to shove at Ron and not take no for an answer. Tell your mum and dad we both came up with it, Harry tells him firmly. Tell them we’re sorry about the car, and this is the best we can do to make up for it.
(In the inevitable kerfuffle Molly then causes around Ron mumbling his way through an explanation of why exactly his parents don’t need to arrange a debt with Mr Ollivander, the old wand is not suitably disposed of. Ron just... shrugs and takes it with him along with his nice new wand because what else do you do with it. And when Lockhart tackles Ron outside the Chamber, Ron, who is supposed to be a quick strategic thinker already capable of outplaying McGonagall in a chess match at eleven and I will die on this fucking hill, is fucking clever enough to switch the old wand from his pocket during their scuffle. Meaning Lockhart comes away with the backfiring wand, which Ron let him grab on purpose, because c’mon guys, Ron really deserves to contribute to the ending of that book in a more meaningful way. Let my boy be capable again.)
2—“And while Harry was sure he had never heard the name T.M. Riddle before, it still seemed to mean something to him, almost as though Riddle was a friend he’d had when he was very small, and half-forgotten.”
If you think I am capable of letting this line pass unremarked, you are wrong. Little Harry locked inside his cupboard talking to and playing with his imaginary friend Tom Riddle. Little Harry who by some miracle managed to not develop severe attachment issues or socially inhibiting maladaptive behaviour patterns or the developmental delays typical of such a harrowing extent of neglect, and is in fact startlingly normal after all that early childhood isolation, do not make me show you the Spitz/Wolf grief film of what happens to babies who lose their parents abruptly and do not experience adequate care replacement, because it turns out he was not actually alone for any of that time and the only thing he couldn't get from his companion was the physical stimulus he needed for his growth indicators to turn out normal. Pseudo-horcrux forced age-regression childhood do-over, I said what I said, and if I can ever get past my own feelings on the matter being so strong they make me weepy just typing it out, I will have one hell of a cathartic time exploring this idea to its deserved extent.
3—Finally, an actually “useless” headcanon (since that is technically the name of the game, so I’d better put at least one on your very generous ask of three): the Potter’s cat was named Marzipan. Marzi, for short. He was Lily’s seventeeth birthday present from her mum and dad. They didn't quite know about the standard coming of age gifts (like certain wonderful metas about women traditionally receiving a locket), but they did know Lily had been begging for a cat ever since her Hogwarts letter told her she could have one. I’m not crying you’re crying