You are very sensible for your age!!!
My priorities are usually shoes and bags. And jewelery. Because a bag will fit no matter what, and so are shoes (unless there is weight gain over 20 kgs, or a pregnancy). Jewelry can even be an investment.
Now taking under consideration your young age, and you are still growing, stick with the bags, if you are not abusing them they will last you for ever. I grew taller when I was 17, and as you can imagine I had to throw away all my old clothes as they didn't fit at all. Imagine I had spent a lot of money on exp jeans, and in like 6 months they didn't fit at all!!!
If I were you I'd stick with less expensive track suits, or mix and match of cheap clothes and a few designer clothes. I usually buy classic stuff of good quality on sale (it's easy for me to find sizes), and I don't spend much on clothing. Plus I only buy clothes 2 times a year and no more than 2-3 garments at a time.
As for my more expensive buys they usually have this pattern: bag, shoes, shoes, accessory, jewelry, bag, shoes, etc... Just to keep a nice balance.