I need help with holiday gift ideas?

I am really excited to buy gifts for my friends this year, but I am unsure what to get them. I have four friends that I am struggling with ideas with, and I was hoping for some help :)

Sarah, 16 : She really likes American Eagle, so I considered a gift card, but I wanted something more personal than that. I also know she likes ice hockey a lot (The capitals)

Kaileigh, 16: She likes anything girly and One Direction, but like the previous, I feel as though it would be hard to get her a unique gift in that area.

Casey, 17: She wants to be a tattoo artist when she's older, I considered getting her a book about it. She's pretty grungey and also likes drawing and painting music, so I considered getting her a record, but her taste is pretty out there.

Kate, 17: She's a huge book worm. I am pretty sure her favourite author is John Green, but she has read all of his books. She's really philosophical and brooding, so I want this gift to mean something.

I would like to keep the price range between $10 - 20. I know this is cheap, but I would like to buy a lot of people at least a little something and I can't afford to get them all lavish gifts. Thanks in advance :)