Received a $15 Barnes and Noble gift card for Christmas. What do I buy?

I normally just get books through the library and really only purchase books that I love and plan on reading again.

I normally read fantasy, science fiction, and mystery/thrillers.

Some of the books on my shelf include: Harry Potter, Lord of the Rings, Hunger Games, the Eragon series, and nearly a shelf full of books written by Mercedes Lackey (fantasy).

Some of the books that I’ve enjoyed but don’t own include: The Red Rising series, books about dystopian/alternate realities, books written by Diane Chamberlin (“normal” fiction with some kind of plot twist), and pretty much anything written by Brandon Sanderson.

I just started the Silo series by Hugh Howey and am hooked already.

I’m open to buying something that I did not list above. Please give me suggestions on what I should get. Fiction only, please.