I am going into my 7th year of teaching first grade and over the years I have added to my library book collection. It's not quite where I want it to be, but it gets better every year.
I have many other book baskets that I will add and change out after I read them. Some books I want to be a surprise. :)
The categories on those baskets are 1. fiction favorites 2. non-fiction 3. holidays ( valentines, st. patricks, etc.) 4. winter 5. fall 6.science 7. social studies
The way I keep all of the books in the correct basket it by colored codes. Each basket a label and on that label there is a colored sticker.
Every book in that basket has the same sticker on it.
So as my students are returning books to and from their read to self baskets they just match up the stickers.
Cheap, simple and keeps our class organized. WIN WIN!