From the beginning of undergraduate school I kept all my papers, handouts, worksheets, etc. that professors provided for me in one big box. Before entering graduate school I organized all the loose papers into categories in a big box so that everything was easy to find. Even when I entered graduate school, I always made one extra copy of activities, handouts, and any resources that I used throughout therapy sessions and grad school classes. I highly recommend keeping everything in notebooks, filing cabinet, boxes, etc, whatever is easiest for you. Start to organize everything from the beginning or at least try, I know it sounds very tedious and I know you have a lot on your plate, but it is definitely worth it in the end. When you start working in your career it is nice to have easy access to all of that great information that you have accumulated over the years. Your professors will give you a lot of great information and you will accumulate a lot of papers over the years, keep it, and file it away in your own "resource box," so that you will always have it. Try not to reuse notebooks if you do not have to, that is half the battle, because it is easier if you just buy a new notebook for a new subject so that you can keep all your papers together.
Also you can organize your documents by uploading them and storing them on an external hard drive.
I provided the pictures above to give you an idea of what my resource box looks like on the outside and then what is on the inside. To the left you can see I put a label on the outside of the box with all the topics that can be found on the inside. To the right is the format that I used on each folder, all the folders are in order by the number.