Google search – use money to buy time instead of stuff
Kids (esp. 15 year old) are at an age that want material things, and I can relate to because many years ago I have been through that age many years ago – I wanted to pick out my own apparel including shoes to impress girls 
But at my current age, I really think opposite: I want to use money to buy time, instead of buy stuff.
Playdate and sleepover
When kids are young, parents sometimes setup playdates for kids.
When kids grow, they want to have their own say and “sleepover” for b-day celebration seems fairly popular among teen girls.
But I realized a few things recently: my 15-year-old would not invite her friends over because out home is much more modest compared to some of her friends. I think to some extent my soon to be 11-year-old felt this way too. So, after about 40 years, my kids end up in similar boat as me – during my middle school and high school years I never invited my friends over too. Different circumstances, obviously, but economy was a factor.
It’s not the end of the world though. On the side of “buying stuff”, if I could go back to it. I felt I am more lenient, or I gave my kids more flexibility compared to what my parents could do back in the day. I told my 15-year-old a story, it was probably when I was a 3rd or 4th grader in the elementary school, and I needed those white tennis shoes for perform (those shoes are somewhat like the low ankle Converse here nowadays, and they are white). I didn’t have those: it would probably cost my parents to sacrifice something else to get the shoes. So my mom borrowed new shoes from a classmate (a girl), and after we used the shoes, my mom washed them and put on some white powder on them, so that they looked like new (or as much as practical).
The other day, I just noticed a girl, friend of my 15-year-old, had the same $100 a pair adidas
Priority
So, the other day, my 15-year-old mentioned she doesn’t have graphing calculator. I mentioned that I offered it to her multiple times. She said she put a hold at the library (I assume the high school library). So, there goes the priority: she put apparel and shoes before the calculator.