I'd say anything he never wishes away he gets to keep. If it's something with a drawback so he ditches it, he obviously doesn't have it anymore.>The truth is that the fairy’s magic is much more powerful than Star’s magic
I'd disagree in some ways. Fairy magic HAS to follow Da Rules, and we know 62 of them with more we don't know but if Timmy tries to cheat they'll be one to stop him. In fact, if Star knows Da Rules she can easily curb-stomp Timmy because some rules are just sort of jokes, but the fact that they exist is still relevant. For example, Rule 12 specifically states (among other things) that you CANNOT affect someone with Fairy magic if they qualify as "those who wear clear glasses as a fashion statement"... which means if Starr shows up to the battle looking like pic related they're fucking worthless against her.
In fact, take a look at Da Rule's article 29... "Fairy magic cannot affect other magical or super-powerful items". Star's wand is already impossible to counter, they can't fucking stop her magic or her other tools like her scissors.
Star can invent her own spells, in fact most of her spells ARE her own inventions. Meanwhile the fairy spells have strict rules even if they have strong base power. Star herself is way more powerful than Timmy, even if she doesn't use her steel-toed pointed boots to make sure he never goes through puberty even without a wish.