I was watching "Less Than Zero" for I don't know how many times now. The Andrew McCarthy character dressed in a way that you knew he was a snot-nosed rich kid. How do they dress now? (if you post pics make sure they are copyright free)
From your example, I take it you're looking for more of a preppy, uppercrust look? Because there are a lot of different rich kid looks; from Eurotrash scene kids to boho-Cochella ones.
As long as you can tell he has money. Also, a pic is one thing but how would you describe it in writing?
The cloths as well. Think he is buying it from top-notch shops. I know there's a video on youtube about this rich child that her mother challenges her to go to a shop buying cheap clothes, but I couldn't find it. But if you do watch the video.
Designer labels would be a big tell. If you say that someone is wearing an archival Givenchy sweater with Diesel pants and Rick Owens high-top sneakers, it's going to be pretty obvious they're rich. The outfit I just described would cost well into thousands of dollars if purchased at their original retail prices. One of my favorite shows right now is Schitt's Creek, about a Kardashian-rich family that loses all their money and possessions and has to live in a small town that they bought as a joke years before. They all walk around this tiny backwoods town in ridiculous designer clothes that are pretty much the only thing they were able to keep. You could do worse than to use the Rose family's wardrobe as inspiration: https://wornontv.net/schitts-creek/ ETA: This is a great article about how the showrunner, Dan Levy, uses fashion to inform his characters: https://www.vulture.com/2018/03/schitts-creek-fashion-looks.html
In my opinion, it would be the most straightforward way. You could also mention that the clothes were purchased in boutiques in, say ,Paris and Milan, or that they were part of a "Spring 2018 resort collection." Anything that references luxury fashion is going to be a shortcut to readers understanding that your character is a spoiled rich kid.