This can be a particularly difficult subject, and not something that can be addressed in just a few paragraphs, so I'm going to address a single idea to start. Parents find that they have to deal with a lot of pressure from kids to buy things in order to "fit in," and parents' own experiences with this sort of pressure often make them inclined to give in. And, based on economic circumstances, a certain level of this may be appropriate, especially in clothing.
However, I don't think you do a child any favors by giving them everything they want and setting no limits. Learning to accept "no" is an important character lesson for adulthood for anyone, no matter how wealthy. I also firmly believe that people will value something far more if they earn it. Yes, parents do assume the responsibility for providing the necessities of life when they choose to have a child. But keep a clear idea between needs, wants, and luxuries. Even the wealthiest child does not NEED more than about a week's worth of everyday clothes and possibly a few additional special items of clothing if that child has social responsibilities for their family.
I believe every child should do some work for their family and understand that that is part of what a family is. Poorer families find the financial burden of peer pressure to dress certain ways very difficult to manage, but reality tends to make most of them find ways to limit it (and I give lots of ideas for that in other posts). Affluent families are often more reluctant to ask children to either limit themselves or earn the extras. But children need limits.
One approach for an affluent family is to set a clear "budget" for clothing for a school year. $500 is more than enough for normal clothing (excluding a winter coat, perhaps), but set a reasonable amount for your income (my kids averaged less than $75 a year including things like shoes and coats). Then give the child the choice. If he or she really wants to spend $125 for a pair of sneakers and $75 for a pair of jeans, he or she is going to be wearing the same clothes over and over a lot. Then offer the opportunity for the child to earn additional money over and above whatever that child normally does for chores to pay for extras.
Learning to make choices is one of the most valuable lessons a child can learn. A child can choose to stay within that budget, buy ordinary clothes and shop sales. Or he or she can shop consignment shops and get great clothes for reasonable prices within that budget. A child can get one or two pricey items and buy cheaper or fewer other clothes to stay within the budget. Or he or she can earn the money to buy the expensive clothes. Myself, I think a child should make no more than minimum wage for household work, which is as much or more than adults make for the same work (and have to complete a job reasonably well) so they appreciate just how much work those items cost---with the bonus that they may learn some empathy for less affluent classmates and resist the urge to join into teasing. It's amazing how many kids suddenly decide those things aren't that important when they stop magically appearing.
My daughters have been shocked to hear college classmates talking about maxing out a credit card over the weekend buying new clothes or having something done to their truck and having to call "Daddy" to pay off the balance so they can spend more. No limits and few repercussions, and usually the same people do the same thing a few weeks later. More telling, these same kids were likely to skip classes, ignore assignments, and show little interest in actually working. After all, they've always been given whatever they wanted, so why should they value the cost of their education? They just have to get by (and sometimes not even that) to meet the minimum requirements of Mom or Dad to keep paying for their 4 or 5 year party, er, education. The thing is, many of these kids will not become responsible adults until they've made major mistakes, and some never will, expecting family to always bail them out.