I feel like Derek would just spoil Stiles rotten! You see Derek never really got to be a teenager courtesy: Kate Argent and well Stiles after his mom's death had to grow up too quickly and then the financial issues of the Stilinski household not to mention his best friend turning into a freakin werewolf! So yeah Stiles didn't get a normal teen life either so you can bet my ass that Derek does everything in his willpower and bank account to remedy that. And he's so extra with it and Stiles just!!
This is such a cute ask!! And it’s absolutely a headcanon of mine that Derek would hate spending his inheritance on himself (see: him having hundreds of thousands of dollars and squatting in an abandoned train depot), and also a headcanon that Laura and Derek had a tradition on spending it on each other on holidays for extravagant things (that’s where the Camaro came from) so Derek buying Stiles nice things or surprising him with expensive trips is just completely fitting to me.
And the thing is, Stiles would probably be put off by it at first. Like… “dude, these are nice but you have me, ok? You don’t need to win me and you definitely don’t need to buy me.” And the ridiculous thing, the thing that makes Stiles feel guilty about all the amazing (and expensive) gestures is that Derek never buys himself anything, never gets anything new for the house or buys himself books or goes out to restaurants unless he thinks Stiles will like them or spends money on anything beyond the bare essentials unless it’s for Stiles or one of the pack.
But eventually I think it would probably click eventually –– when Derek’s planning a trip to the Caymans because “Stiles, you like beaches and the water’s incredible there, look at these pictures, and see, you can swim over the reefs and there’s a boat trip to pet stingrays, you’ll like that” –– that Derek’s not doing any of this to buy Stiles, or because he thinks he has to impress Stiles with expensive things to keep him, or even necessarily for Stiles. Yes, he genuinely thinks Stiles would like the trip, and Stiles is sure he will, but Derek’s face has just this little hint of shy excitement when he’s talking about stingrays and about all the water activities they can do… and Stiles realizes that this is something Derek really wants to do. For Derek.
And he probably also really wanted to try out that nice restaurant last week –– the one that was strangely fancy and lacking in burgers, considering Derek had framed it as a “place Stiles would love,” and Derek has spent a hell of a lot more time on that porch swing than Stiles ever has, even though Derek had made it so Stiles “would have a place to sit if the pack was ever out back training.”
Derek does buy himself things, sometimes, slipped in between the newest Playstation and the trip to Comic Con and all the things that are genuinely and truly meant just to brighten Stiles’ life. He just doesn’t know how to say that –– to admit it to even himself, maybe. To give anything nice to himself, because he still doesn’t feel, deep down, like he deserves it.
So Stiles lets Derek book that trip, and the stingray boat ride, even though he’d really rather stay at the beach and not risk his life to stinging, thank you very much. And he stops complaining when Derek buys him expensive things –– buys them expensive things –– loving the little moments where Derek buys something that’s just clearly not Stiles-centric for the thrill of watching Derek indulge himself, even secretly.