When I was younger, there was only a few things in my bag, essentially because I had no idea what to do with everything else. I had the basics: black eyeliner, lipstick, and maybe mascara. At that age, that was really all I needed because I still had that even skintone.
Over the years my skin started to form blotches, freckles, and omg bags! (I'm still beautiful, though;) I then began to learn about the importance of concealor, foundation, powder, blush, and so on.
My niece is at the age where she is experimenting with make-up, so I got her a basic starter kit and put together a list of items that she should have for that everyday natural look. I got her the "Flawless Face Kit" by Laura Mercier, and one of the holiday brush sets from Mac (that are now 25% off). She is 17 and still has that fresh face look, so I didn't recommend wearing makeup daily for her. At this age all she needs is a good moisturizer, lip gloss, mascara, and a natural blush.
Here is a list of items every girl should have. Check back later for a break down of these items and why they are important.