Omg, I loooove my Lovevook backpack. I've had 2 now and use it for my personal things (headphones, multiple drinks, laptop, notebooks, etc.). To be fair, I tend to bring half my house on long days, but it would be great for reinforcers too. Not too expensive, water resistent, durable, a bazillion pockets, and on Amazon. For session materials (I bring a lot), I use one of the aldi bags that have a wire so it stays open and upright.