We submitted ours in July and still the school has no idea what they are doing.
Chances are they do, they're just probably finalising the timetable for next year before they scream out and say you have x y z subjects.
Realities of backend admin processes that you don't see day-to-day as a student..
Does your school run like a Headstart program for your next year's subjects (ideally starting very soon if not now?) - I am speaking from personal experience here so don't quote me on it, but there is an assumption that you won't have books until next year anyway (unless of course it's english where you have to read over the holidays etc). Booklist dates are usually in the early part of the new year. I know at my school for a subject like maths we print off anything students need in the meantime.
Personally wouldn't be going out and buying anything until your subjects are confirmed.